🏣 Clean up for arxiv

book/ebook_src/real_interview_problems/2n_packets.py

@@ -0,0 +1,41 @@
+#!/bin/python
+
+import math
+import os
+import random
+import re
+import sys
+
+# Complete the 'largestRepackaged' function below.
+#
+# The function is expected to return a LONG_INTEGER.
+# The function accepts INTEGER_ARRAY arrivingPackets as parameter.
+#
+
+def largestRepackaged(arrivingPackets):
+
+    packet_size = arrivingPackets[0]
+    packets = arrivingPackets[1:]
+    largest_packet = 0
+    remaining = 0
+
+    for packet in packets:
+        print packet
+        if remaining:
+            packet += remaining
+            remaining = 0
+
+        if packet % 2 != 0:
+            remaining = packet % 2 
+            packet -= remaining
+        
+        if packet > largest_packet:
+            largest_packet = packet
+
+    return largest_packet
+
+
+if __name__ == '__main__':
+    arrivingPackets= [5, 1, 2, 4, 7, 5]
+   
+    print(largestRepackaged(arrivingPackets))

book/ebook_src/real_interview_problems/balanced.py

@@ -0,0 +1,22 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+def balance_par_str_with_stack(str1):
+    i, stack = 0, []
+
+    while i < len(str1):
+        symbol = str1[i]
+        if symbol == "(":
+            stack.append(symbol)
+        elif symbol == ")":
+            stack.pop()
+        i += 1
+    return not stack
+
+
+
+if __name__ == '__main__':
+    print(balance_par_str_with_stack('((()))'))
+    print(balance_par_str_with_stack('(()'))

book/ebook_src/real_interview_problems/binary_search.py

@@ -0,0 +1,50 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+def binary_search(array, value):   
+    last, first = len(array), 0
+    
+    while first < last:
+        mid = (last - first)//2
+        item = array[mid]
+        
+        if item == value:
+            return True
+        
+        elif item < value:
+            last = mid
+        
+        else:
+            first = mid 
+    
+    return False
+
+def binary_search_rec(array, value, first=0, last=None):
+    last = last or len(array)
+    if len(array[first:last]) < 1:
+        return False
+    
+    mid = (last - first)//2
+    if array[mid] == value:
+        return True
+    elif array[mid] < value:
+        return binary_search_rec(array, value, first=first, last=mid)
+    else:
+        return binary_search_rec(array, value, first=mid, last=last)
+
+    
+if __name__ == '__main__':    
+    array = [3, 4, 6, 7, 10, 11, 34, 67, 84]
+    value = 6
+    assert(binary_search(array, value) == True)   
+    assert(binary_search_rec(array, value) == True)  
+    value = 8
+    assert(binary_search(array, value) == False)
+    assert(binary_search_rec(array, value) == False)  
+    array = [8]
+    assert(binary_search(array, value) == True)
+    assert(binary_search_rec(array, value) == True)  
+    array = []
+    assert(binary_search(array, value) == False)
+    assert(binary_search_rec(array, value) == False)  

book/ebook_src/real_interview_problems/bst.py

@@ -0,0 +1,165 @@
+#!/usr/bin/python
+
+__author__ = "bt3"
+
+from collections import deque
+
+class Node(object):
+
+    def __init__(self, item=None):
+
+        self.item = item
+        self.left = None
+        self.right = None
+
+
+    def _add(self, value):
+        new_node = Node(value)
+        if not self.item:
+            self.item = new_node
+        else:
+            if value > self.item:
+                self.right = self.right and self.right._add(value) or new_node
+            elif value < self.item:
+                self.left = self.left and self.left._add(value) or new_node
+            else:
+                print("BSTs do not support repeated items.")
+        return self 
+
+
+    def _search(self, value):
+        if self.item == value:
+            return True 
+        elif self.left and value < self.item:
+                return self.left._search(value)
+        elif self.right and value > self.item:
+                return self.right._search(value)
+        else:
+            return False
+
+
+    def _isLeaf(self):
+        return not self.right and not self.left
+
+
+    def _printPreorder(self):
+        print self.item
+
+        if self.left:
+            self.left._printPreorder()
+
+        if self.right:
+            self.right._printPreorder()
+
+            
+    def _preorder_array(self):
+        nodes = []
+        if self.item:
+            nodes.append(self.item)
+        if self.left:
+            nodes.extend(self.left._preorder_array())
+        if self.right:
+            nodes.extend(self.right._preorder_array())
+        return nodes
+
+
+
+class BST(object):
+
+    def __init__(self):
+        self.root = None
+
+    def add(self, value):
+        if not self.root:
+            self.root = Node(value)
+        else:
+            self.root._add(value)
+
+    def printPreorder(self):
+        if self.root:
+            self.root._printPreorder()
+
+    def search(self, value):
+        if self.root:
+            return self.root._search(value)
+
+    def preorder_array(self):
+        if self.root:
+            return self.root._preorder_array()
+        else:
+            return 'Tree is empty.'
+
+
+
+
+def BFT(tree):
+    current = tree.root
+    nodes = []
+    queue = deque()
+    queue.append(current)
+
+    while queue:
+        current = queue.popleft()
+        nodes.append(current.item)
+        if current.left:
+            queue.append(current.left)
+        if current.right:
+            queue.append(current.right)
+
+    return nodes
+
+
+def preorder(tree, nodes=None):
+    nodes = nodes or []
+    if tree:
+        nodes.append(tree.item)
+        if tree.left:
+            preorder(tree.left, nodes)
+        if tree.right:
+            preorder(tree.right, nodes)
+    return nodes
+
+
+def postorder(tree, nodes=None):
+    nodes = nodes or []
+    if tree:
+        if tree.left:
+            nodes = postorder(tree.left, nodes)
+        if tree.right:
+            nodes = postorder(tree.right, nodes)
+        nodes.append(tree.item)
+
+    return nodes
+
+
+def inorder(tree, nodes=None):
+    nodes = nodes or []
+    if tree:
+        if tree.left:
+            nodes = inorder(tree.left, nodes)
+        nodes.append(tree.item)
+        if tree.right:
+            nodes = inorder(tree.right, nodes)
+    return nodes
+
+
+        
+        
+if __name__ == '__main__':
+    bst = BST()
+    l = [10, 5, 6, 3, 8, 2, 1, 11, 9, 4]
+    for i in l:
+        bst.add(i)
+
+    print
+    print "Searching for nodes 16 and 6:"
+    print bst.search(16)
+    print bst.search(6)
+
+    print
+    print 'Traversals:'
+    print 'Original:    ', l
+    print 'Preorder:    ', preorder(bst.root)
+    print 'Postorder:   ', postorder(bst.root)
+    print 'Inorder:     ', inorder(bst.root)
+    print 'BSF:         ', BFT(bst)

book/ebook_src/real_interview_problems/check_anagram.py

@@ -0,0 +1,38 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+from collections import Counter
+
+def check_if_anagram(word1, word2):
+    counter = Counter()
+    
+    for c in word1:
+        counter[c] += 1
+    
+    for c in word2:
+        counter[c] -= 1
+        
+    for values in counter.values():
+        if values != 0:
+            return False
+
+    return True
+    
+    
+    
+if __name__ == '__main__':
+    word1 = 'abc'
+    word2 = 'bca'
+    assert(check_if_anagram(word1, word2) == True)
+    
+    word2 = 'bcd'
+    assert(check_if_anagram(word1, word2) == False)
+    
+    word1 = ''
+    word2 = ''
+    assert(check_if_anagram(word1, word2) == True)
+    
+    word1 = 'a'
+    word2 = 'a'
+    assert(check_if_anagram(word1, word2) == True)

book/ebook_src/real_interview_problems/combination.py

@@ -0,0 +1,32 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+def combination(array):
+    if len(array) < 2:
+        return set(array)
+    
+    result = set()
+    for index, item in enumerate(array):
+        new_array = array[:index] + array[index+1:]
+        result.add(item)
+        for perm in combination(new_array):
+            new_item = ''.join(sorted(item + perm))
+            result.add(new_item)
+    
+    return result
+    
+    
+    
+if __name__ == '__main__':
+    array = ['a', 'b', 'c']
+    result = set(['a', 'ac', 'ab', 'abc', 'bc', 'c', 'b']) 
+    assert(combination(array) == result)
+    
+    array = ['']
+    result = set([''])
+    assert(combination(array) == result)
+    
+    array = ['a']
+    result = set(['a'])
+    assert(combination(array) == result)

book/ebook_src/real_interview_problems/hash_table.py

@@ -0,0 +1,45 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+class HashTable(object):
+    def __init__(self, slots=10):
+        self.slots = slots
+        self.table = []
+        self.create_table()
+
+    # Get the slot
+    def hash_key(self, value):
+        return hash(value)%self.slots
+
+    # When creating the table, add list struct 
+    # to each slot
+    def create_table(self):
+        for i in range(self.slots):
+            self.table.append([])
+
+    # Method to add a item in the right slot
+    def add_item(self, value):
+        key = self.hash_key(value)
+        self.table[key].append(value)
+
+    # Aux: print table
+    def print_table(self):
+        for key in range(self.slots):
+            print "Key is {0}, value is {1}.".format(key, self.table[key])
+
+    # Aux: find item
+    def find_item(self, item):
+        item_hash = self.hash_key(item)
+        return item in self.table[item_hash]
+        
+
+if __name__ == '__main__':
+    dic = HashTable(5)
+    for i in range(1, 40, 2):
+        dic.add_item(i)
+
+    dic.print_table()
+    assert(dic.find_item(20) == False)
+    assert(dic.find_item(21) == True)

book/ebook_src/real_interview_problems/linked_list.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+class Node(object):
+    def __init__(self, value, next=None):
+        self.value = value
+        self.next = next
+        
+
+class LinkedList(object):
+    def __init__(self):
+        self.head = None
+  
+      def _add(self, value):
+        self.head = Node(value, self.head)
+            
+    def _printList(self):
+        node = self.head
+        while node:
+            print node.value
+            node = node.next
+            
+    def _find(self, index):
+        prev = None
+        node = self.head
+        i = 0
+        while node and i < index:
+            prev = node
+            node = node.next
+            i += 1
+        return node, prev, i
+
+    def _delete(self, prev, node):
+        if not prev:
+            self.head = node.next
+        else:
+            prev.next = node.next
+    
+    def deleteNode(self, index):
+        node, prev, i = self._find(index)
+        if index == i:
+            self._delete(prev, node)
+        else:
+            print('Node with index {} not found'.format(index))
+
+    
+
+if __name__ == '__main__':
+    ll = LinkedList()
+    for i in range(1, 5):
+        ll._add(i)
+        
+    print('The list is:')
+    ll._printList()
+     
+    print('The list after deleting node with index 2:')
+    ll.deleteNode(2)
+    ll._printList()

book/ebook_src/real_interview_problems/longest_common_prefix.py

@@ -0,0 +1,32 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+def longest_common_substring(s1, s2):
+    p1 = 0
+    aux, lcp = '', ''
+    string1 = max(s1, s2)
+    string2 = min(s1, s2)
+
+    while p1 < len(string1):
+        p2 = 0
+        while  p2 < len(string2) and p1+p2 < len(string1):
+            if string1[p1+p2] == string2[p2]:
+                aux += string1[p1+p2]
+            else:
+                if len(lcp) < len(aux):
+                    lcp = aux
+                aux = ''
+            p2 += 1
+        p1 += 1
+
+    return lcp
+             
+    
+    
+if __name__ == '__main__':
+    str1 = 'hasfgeaae'
+    str2 = 'bafgekk'
+    result = 'fge'
+    assert(longest_common_substring(str1, str2) == result)

book/ebook_src/real_interview_problems/longest_increasing_subsequence.py

@@ -0,0 +1,31 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+def longest_increasing_subsequence(seq):
+    result, aux = [], []
+    seq.append(-float('infinity'))
+    
+    for i, value in enumerate(seq[:-1]):
+        aux.append(value)
+        if value > seq[i+1]:
+            if len(result) < len(aux):
+                result = aux[:]
+            aux = []
+    return result
+             
+    
+    
+if __name__ == '__main__':
+    seq = [10, -12, 2, 3, -3, 5, -1, 2, -10]
+    result = [-12, 2, 3]
+    assert(longest_increasing_subsequence(seq) == result)
+    
+    seq = [2]
+    result = [2]
+    assert(longest_increasing_subsequence(seq) == result)
+
+    seq = []
+    result = []
+    assert(longest_increasing_subsequence(seq) == result)

book/ebook_src/real_interview_problems/merge_sort.py

@@ -0,0 +1,47 @@
+#!/usr/bin/env python
+# AKA: do you believe in magic?
+
+__author__ = "bt3"
+
+def merge_sort(array):
+    if len(array) < 2:
+        return array
+    
+    # divide
+    mid = len(array)//2
+    left = merge_sort(array[:mid])
+    right = merge_sort(array[mid:])
+    
+    # merge
+    result = []
+    i, j = 0, 0
+    
+    while i < len(left) and j < len(right):
+        if left[i] < right[j]:
+            result.append(left[i])
+            i += 1
+        else:
+            result.append(right[j])
+            j+= 1
+    
+    # make sure nothing is left behind
+    if left[i:]:
+        result.extend(left[i:])
+    if right[j:]:
+        result.extend(right[j:])
+    
+    return result
+    
+    
+    
+    
+if __name__ == '__main__':
+    array = [3, 1, 6, 0, 7, 19, 7, 2, 22]
+    sorted = [0, 1, 2, 3, 6, 7, 7, 19, 22]
+    assert(merge_sort(array) == sorted)
+    
+    array = []
+    assert(merge_sort(array) == array)
+
+    array = [1]
+    assert(merge_sort(array) == array)

book/ebook_src/real_interview_problems/other_resources/PYTHON.md

@@ -0,0 +1,281 @@
+
+## Python General Questions & Answers
+
+Python is a programming language with objects, modules, threads, exceptions and automatic memory management. The benefits of pythons are that it is simple and easy, portable, extensible, build-in data structure and it is an open source.
+
+
+#### What is PEP 8?
+
+PEP 8 is a coding convention, a set of recommendation, about how to write your Python code more readable.
+
+
+#### What is pickling and unpickling?
+
+Pickle module accepts any Python object and converts it into a string representation and dumps it into a file by using a dump function, this process is called pickling. While the process of retrieving original Python objects from the stored string representation is called unpickling.
+
+
+#### How Python is interpreted?
+
+Python language is an interpreted language. Python program runs directly from the source code. It converts the source code that is written by the programmer into an intermediate language, which is again translated into machine language that has to be executed.
+
+
+#### How memory is managed in Python?
+
+Python memory is managed by Python private heap space. All Python objects and data structures are located in a private heap. The programmer does not have access to this private heap and interpreter takes care of this Python private heap.
+The allocation of Python heap space for Python objects is done by Python memory manager. The core API gives access to some tools for the programmer to code.
+Python also has an inbuilt garbage collector, which recycle all the unused memory and frees the memory and makes it available to the heap space.
+
+
+#### What are the tools that help to find bugs or perform static analysis?
+
+PyChecker is a static analysis tool that detects the bugs in Python source code and warns about the style and complexity of the bug. Pylint is another tool that verifies whether the module meets the coding standard.
+
+
+#### What are Python decorators?
+
+A Python decorator is a specific change that we make in Python syntax to alter functions easily.
+
+#### What is the difference between list and tuple?
+
+The difference between list and tuple is that list is mutable while tuple is not. Tuple can be hashed for e.g as a key for dictionaries.
+
+
+#### How are arguments passed by value or by reference?
+
+Everything in Python is an object and all variables hold references to the objects. The references values are according to the functions; as a result, you cannot change the value of the references. However, you can change the objects if it is mutable.
+
+
+
+#### What are the built-in type does python provides?
+
+There are mutable and Immutable types of Pythons built-in types Mutable built-in types
+
+List
+Sets
+Dictionaries
+Immutable built-in types
+Strings
+Tuples
+Numbers
+
+
+#### What is namespace in Python?
+
+In Python, every name introduced has a place where it lives and can be hooked for. This is known as namespace. It is like a box where a variable name is mapped to the object placed. Whenever the variable is searched out, this box will be searched, to get the corresponding object.
+
+
+#### What is lambda in Python?
+
+It is a single expression anonymous function often used as an inline function.
+
+
+#### Why lambda forms in python do not have statements?
+
+A lambda form in python does not have statements as it is used to make new function object and then return them at runtime.
+
+
+#### What is pass in Python?
+
+Pass means, no-operation Python statement, or in other words, it is a place holder in a compound statement, where there should be a blank left and nothing has to be written there.
+
+
+
+#### In Python what are iterators?
+
+In Python, iterators are used to iterate a group of elements, containers like list.
+
+
+#### What is unittest in Python?
+
+A unit testing framework in Python is known as unittest. It supports sharing of setups, automation testing, shutdown code for tests, aggregation of tests into collections, etc.
+
+
+#### In Python what is slicing?
+
+A mechanism to select a range of items from sequence types like list, tuple, strings, etc. is known as slicing.
+
+
+#### What are generators in Python?
+
+The way of implementing iterators are known as generators. It is a normal function except that it yields expression in the function.
+
+
+#### What is docstring in Python?
+
+A Python documentation string is known as docstring, it is a way of documenting Python functions, modules and classes.
+
+
+#### How can you copy an object in Python?
+
+To copy an object in Python, you can try copy.copy () or copy.deepcopy() for the general case. You cannot copy all objects but most of them.
+
+#### What is the difference between deep and shallow copy?
+
+Shallow copy is used when a new instance type gets created and it keeps the values that are copied in the new instance. Whereas, a deep copy is used to store the values that are already copied.
+
+#### What is a negative index in Python?
+
+Python sequences can be index in positive and negative numbers. For positive index, 0 is the first index, 1 is the second index and so forth. For negative index, (-1) is the last index and (-2) is the second last index and so forth.
+
+
+#### How you can convert a number to a string?
+
+In order to convert a number into a string, use the inbuilt function str(). If you want a octal or hexadecimal representation, use the inbuilt function oct() or hex().
+
+
+#### What is the difference between Xrange and range?
+
+Xrange returns the xrange object while range returns the list, and uses the same memory no matter what the range size is.
+
+
+#### What is module and package in Python?
+
+In Python, a module is the way to structure program. Each Python program file is a module, which imports other modules like objects and attributes.
+The folder of Python program is a package of modules. A package can have modules or subfolders.
+
+
+#### What are the rules for local and global variables in Python?
+
+Local variables: If a variable is assigned a new value anywhere within the function's body, it's assumed to be local.
+
+Global variables: Those variables that are only referenced inside a function are implicitly global.
+
+
+#### How can you share global variables across modules?
+
+To share global variables across modules within a single program, create a special module. Import the config module in all modules of your application. The module will be available as a global variable across modules.
+
+
+#### Explain how can you make a Python Script executable on Unix?
+
+To make a Python Script executable on Unix, you need to do two things,
+
+Script file's mode must be executable and
+the first line must begin with # (`#!/usr/local/bin/python`).
+
+
+#### Explain how to delete a file in Python?
+
+By using a command `os.remove (filename)` or `os.unlink(filename)`.
+
+
+#### Explain how can you generate random numbers in Python?
+
+To generate random numbers in Python, you need to import command as
+
+```
+import random
+random.random()
+```
+
+This returns a random floating point number in the range [0,1)
+
+
+#### Explain how can you access a module written in Python from C?
+
+You can access a module written in Python from C by following method,
+
+```
+Module = =PyImport_ImportModule("<modulename>");
+```
+
+
+#### Mention the use of // operator in Python?
+
+It is a Floor Division operator, which is used for dividing two operands with the result as quotient showing only digits before the decimal point. For instance, `10//5 = 2 and 10.0//5.0 = 2.0`.
+
+
+#### Explain what is Flask & its benefits?
+
+Flask is a web microframework for Python based on "Werkzeug, Jinja 2 and good intentions" BSD licensed. Werkzeug and jingja are two of its dependencies.
+
+Flask is part of the micro-framework. Which means it will have little to no dependencies on external libraries. It makes the framework light while there is a little dependency to update and fewer security bugs.
+
+
+#### What is the difference between Django, Pyramid, and Flask?
+
+Flask is a "microframework" primarily build for a small application with simpler requirements. In Flask, you have to use external libraries. Flask is ready to use.
+
+Pyramid is built for larger applications. It provides flexibility and lets the developer use the right tools for their project. The developer can choose the database, URL structure, templating style and more. Pyramid is heavy configurable.
+
+Like Pyramid, Django can also be used for larger applications. It includes an ORM.
+
+
+#### Explain how you can access sessions in Flask?
+
+A session basically allows you to remember information from one request to another. In a flask, it uses a signed cookie so the user can look at the session contents and modify. The user can modify the session if only it has the secret key Flask.secret_key.
+
+
+#### Is Flask an MVC model and if yes give an example showing MVC pattern for your application?
+
+Basically, Flask is a minimalistic framework which behaves the same as MVC framework. So MVC is a perfect fit for Flask, and the pattern for MVC we will consider for the following example:
+
+```python
+from flask import Flask
+
+app = Flask(_name_)
+
+@app.route("/")
+
+Def hello():
+
+return "Hello World"
+
+app.run(debug = True)
+```
+
+#### Explain database connection in Python Flask?
+
+Flask supports database powered application (RDBS). Such a system requires creating a schema, which requires piping the shema.sql file into a sqlite3 command. So you need to install sqlite3 command in order to create or initiate the database in Flask.
+
+Flask allows requesting database in three ways
+
+* before_request() : They are called before a request and pass no arguments.
+* after_request() : They are called after a request and pass the response that will be sent to the client.
+* teardown_request(): They are called in a situation when an exception is raised, and response is not guaranteed. They are called after the response been constructed. They are not allowed to modify the request, and their values are ignored.
+
+
+
+#### You are having multiple Memcache servers running Python, in which one of the Memcache server fails, and it has your data, will it ever try to get key data from that one failed server?
+
+The data in the failed server won't get removed, but there is a provision for auto-failure, which you can configure for multiple nodes. Fail-over can be triggered during any kind of socket or Memcached server level errors and not during normal client errors like adding an existing key, etc.
+
+
+#### Explain how you can minimize the Memcached server outages in your Python Development?
+
+When one instance fails, several of them goes down, this will put a larger load on the database server when lost data is reloaded as the client make a request. To avoid this, if your code has been written to minimize cache stampedes then it will leave a minimal impact.
+
+Another way is to bring up an instance of Memcached on a new machine using the lost machines IP address.
+
+
+#### Explain how Memcached should not be used in your Python project?
+
+Memcached common misuse is to use it as a data store, and not as a cache. Never use Memcached as the only source of the information you need to run your application. Data should always be available through another source as well. Memcached is just a key or value store and cannot perform query over the data or iterate over the contents to extract information. Memcached does not offer any form of security either in encryption or authentication.
+
+#### What's a metaclass in Python?
+
+This type of class holds the instructions about the behind-the-scenes code generation that you want to take place when another piece of code is being executed. With a metaclass, we can define properties that should be added to new classes that are defined in our code.
+
+#### Why isn't all memory freed when Python exits?
+Objects referenced from the global namespaces of Python modules are not always deallocated when Python exits. This may happen if there are circular references. There are also certain bits of memory that are allocated by the C library that are impossible to free/ Python is, however, aggressive about cleaning up memory on exit and does try to destroy every single object.
+
+If you want to force Python to delete certain things on deallocation, you can use the atexit module to register one or more exit functions to handle those deletions.
+
+#### Usage of `__slots__`?
+
+The special attribute `__slots__` allows you to explicitly state which instance attributes you expect your object instances to have, with the expected results:
+
+* faster attribute access.
+* space savings in memory.
+
+#### What id() function in Python is for?
+
+`id()` function accepts a single parameter and is used to return the identity of an object. This identity has to be unique and constant for this object during the lifetime. Two objects with non-overlapping lifetimes may have the same `id()` value.
+
+#### Is Python call-by-value or call-by-reference? 
+
+Neither. In Python, (almost) everything is an object. What we commonly refer to as "variables" in Python are more properly called names. Likewise, "assignment" is really the binding of a name to an object. Each binding has a scope that defines its visibility, usually the block in which the name originates.
+
+In Python a variable is not an alias for a location in memory. Rather, it is simply binding to a Python object.ext post.
+
+----

book/ebook_src/real_interview_problems/other_resources/Project-Euler/.gitignore

@@ -0,0 +1,44 @@
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+env/
+build/
+develop-eggs/
+dist/
+eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+*.egg-info/
+.installed.cfg
+*.egg
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.coverage
+.cache
+nosetests.xml
+coverage.xml
+
+# Translations
+*.mo
+*.pot
+
+# Django stuff:
+*.log
+
+# Sphinx documentation
+docs/_build/

book/ebook_src/real_interview_problems/other_resources/Project-Euler/001-multiples_of_3_and_5.py

@@ -0,0 +1,22 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+
+def mul3and5(n):
+    result = 0
+    for num in range(1, n):
+        if num%3 == 0 or num%5 == 0:
+            result += num
+    return result
+      
+    
+    
+def test_():
+    assert(mul3and5(10) == 23)
+    print(mul3and5(1000))
+    print('Tests Passed!')
+            
+if __name__ == '__main__':
+    test_()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/002-even_fib_num.py

@@ -0,0 +1,18 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+   
+def even_fib_num(limit):
+    a, b = 0, 1
+    while a < limit:
+        yield a
+        a, b = b, a + b
+
+def main():
+    print(sum(n for n in even_fib_num(4e6) if not (n & 1)))
+    print('Tests Passed!')
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/003-largest_prime_factor.py

@@ -0,0 +1,41 @@
+#!/usr/bin/python3
+#!/usr/bin/python3
+
+def is_prime(n):
+    if n < 4 : return True
+    for i in range(2, int(n**0.5 + 1)):
+        if not n%i: return False
+    return True
+
+
+def largest_prime_factor(n):
+    i = int(n**0.5 +1)
+    while i > 1 :
+        if not n%i and i&1: 
+            if is_prime(i): return i
+        i -= 1
+    return None
+
+
+def largest_prime_factor_optimized(n):
+    factor = 2
+    lastfactor = 1
+    while n > 1:
+        if not n%factor:
+            lastfactor = factor
+            n = n//factor
+            while n%factor == 0:
+                n = n//factor
+        factor += 1      
+    return lastfactor
+
+
+def test_largest_prime_factor():
+    assert(largest_prime_factor(13195)== 29)
+    print(largest_prime_factor(600851475143))  
+    assert(largest_prime_factor_optimized(13195) == 29)
+    print(largest_prime_factor_optimized(600851475143))  
+    print('Tests Passed!')
+            
+if __name__ == '__main__':
+    test_largest_prime_factor()

book/ebook_src/real_interview_problems/other_resources/Project-Euler/004-larg_palindrome.py

@@ -0,0 +1,47 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+
+
+def is_palindrome(s):
+    return s == reverse(s)
+
+def reverse(s):
+    rev = 0
+    while s > 0:
+        rev = 10*rev + s%10
+        s = s//10
+    return rev
+
+
+def is_palindrome_2(s):
+    # to use it you need to cast str() first
+    while s:
+        if s[0] != s[-1]: return False
+        else:
+            s = s[1:-1] 
+            is_palindrome(s)
+    return True
+
+
+def larg_palind_product(n):
+    nmax, largpal = 9, 0
+    for i in range(1, n):
+       nmax += 9*10**i
+    for i in range(nmax, nmax//2, -1):
+        for j in range(i -1, (i -1)//2, -1):
+            candidate = i*j
+            if is_palindrome(candidate) and candidate > largpal:
+                largpal = candidate
+    return largpal
+
+
+def test_larg_palind_product():
+    assert(larg_palind_product(2)== 9009)
+    print(larg_palind_product(3))
+    print('Tests Passed!')
+            
+if __name__ == '__main__':
+    test_larg_palind_product()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/005-smallest_multiple.py

@@ -0,0 +1,32 @@
+#!/usr/bin/python3
+
+def smallest_multiple(n):
+    set1 = set([x for x in range(1, n+1)])
+    set2 = set()
+    for i in range(len(set1), 0, -1):
+        for j in range(1, i):
+            if i%j == 0:
+                set2.add(j)
+    set1 = set1 - set2 
+    res_num = n*n   
+    while True:
+        for i in set1:
+            missing_div = False
+            if res_num%i: 
+                missing_div = True
+                shift = res_num%i
+                break       
+        if not missing_div: return res_num
+        res_num += 1 or shift
+        shift = 0
+        
+        
+
+
+def test_():
+    assert(smallest_multiple(10) == 2520)
+    print(smallest_multiple(20))
+    print('Tests Passed!')
+            
+if __name__ == '__main__':
+    test_()

book/ebook_src/real_interview_problems/other_resources/Project-Euler/006-sum_square_diff.py

@@ -0,0 +1,21 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+   
+def sum_square_diff(n):
+    sq_sum, sum_sq = 0, 0
+    for i in range(1, n+1):
+        sum_sq += i**2
+        sq_sum += i
+    sq_sum = sq_sum **2
+    return sq_sum - sum_sq
+
+def main():
+    assert(sum_square_diff(10) == 2640)
+    print(sum_square_diff(100))
+    print('Tests Passed!')
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/007-findstprime.py

@@ -0,0 +1,32 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+import math
+   
+def is_prime(number, prime_set):
+    if number in prime_set: return True
+    for i in range(2, int(math.sqrt(number)) + 1):
+        if not number%i: return False
+    return True
+    
+    
+def findstprime(n):
+    count = 0
+    candidate = 1
+    prime_set = set()
+    while count < n: 
+        candidate +=1 
+        if is_prime(candidate, prime_set):
+            prime_set.add(candidate)
+            count += 1       
+    return candidate
+
+def main():
+    assert(findstprime(6 == 13))
+    print(findstprime(10001))
+    print('Tests Passed!')
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/008-largest_product_seq.py

@@ -0,0 +1,28 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+
+   
+def largest_prod_seq(n):
+    result = 0
+    for i in range(0, len(n)-4):
+        first = int(n[i])
+        second = int(n[i+1])
+        third = int(n[i+2])
+        fourth = int(n[i+3])
+        fifth = int(n[i+4])
+        result_here =  first*second*third*fourth*fifth
+        if result < result_here: 
+            result = result_here 
+    return result
+    
+
+def main():
+    n = '7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450'
+    print(largest_prod_seq(n))
+    print('Tests Passed!')
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/009-special_pyt.py

@@ -0,0 +1,26 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+
+   
+def special_pyt(n):
+    for i in range(3, n):
+        for j in range(i+1, n):
+            c = calc_c(i,j)
+            if i + j + c == n: 
+                return i*j*c
+
+def calc_c(a, b):
+    return (a**2 + b**2)**0.5
+
+    
+
+def main():
+    assert(special_pyt(3+4+5) == (3*4*5))
+    print(special_pyt(1000))
+    print('Tests Passed!')
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/010-summation_primes.py

@@ -0,0 +1,24 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+from findstprime import is_prime
+   
+def summation_primes(n):
+    candidate = 2
+    prime_set = set()
+    while candidate < n:    
+        if is_prime(candidate, prime_set):
+            prime_set.add(candidate)
+        candidate +=1 
+    return sum(prime_set)              
+
+
+def main():
+    assert(summation_primes(10) == 17)
+    print(summation_primes(2000000))
+    print('Tests Passed!')
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/011-larg_prod_grid.py

@@ -0,0 +1,66 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+import string
+
+def get_grid(filename):
+    grid = [ [ 0 for i in range(20) ] for j in range(20) ]
+    with open(filename) as file:
+        for row, line in enumerate(file):
+            line.strip('\n')
+            for collumn, number in enumerate(line.split(' ')):
+                grid[row][collumn] = int(number)
+    return grid
+
+
+def larg_prod_grid(grid):
+    row, col, larg_prod = 0, 0, 0
+    up, down, left, right, diag1, diag2, diag3, diag4 = 0, 0, 0, 0, 0, 0, 0, 0
+    while row < len(grid):
+        while col < len(grid[0]):           
+            if col > 2: 
+                up = grid[row][col] * grid[row][col-1] * grid[row][col-2] * grid[row][col-3]
+            if col <  len(grid[0]) - 3:
+                down = grid[row][col] * grid[row][col+1] * grid[row][col+2] * grid[row][col+3]
+            if row > 2:
+                left = grid[row][col] * grid[row-1][col] * grid[row-2][col] * grid[row-3][col]
+            if row <  len(grid) - 3:
+                right = grid[row][col] * grid[row+1][col] * grid[row+2][col] * grid[row+3][col]
+            
+            if col > 2 and row > 2:
+                diag1 = grid[row][col] * grid[row-1][col-1] * grid[row-2][col-2] * grid[row-3][col-3]       
+            if col > 2 and row <  len(grid) - 3:
+                diag2 = grid[row][col] * grid[row+1][col-1] * grid[row+2][col-2] * grid[row+3][col-3]
+            
+            if col <  len(grid[0]) - 3 and row > 2:
+                diag3 = grid[row][col] * grid[row-1][col+1] * grid[row-2][col+2] * grid[row-3][col+3]    
+            if col <  len(grid[0]) -3 and   row <  len(grid) - 3:
+                down = grid[row][col] * grid[row+1][col+1] * grid[row+1][col+2] * grid[row+1][col+3]
+            
+            l1 = [up, down, left, right, diag1, diag2, diag3, diag4]
+            largest_prod_here = max(l1)
+            if largest_prod_here > larg_prod:
+                larg_prod = largest_prod_here 
+            col += 1
+        col = 0
+        row += 1
+   
+    return larg_prod
+
+    
+def main():
+    import time
+    start = time.time() 
+     
+    filename = 'larg_prod_grid.dat'
+    grid = get_grid(filename)
+    assert((grid[6][8], grid[7][9], grid[8][10], grid[9][11]) == (26, 63, 78, 14))
+    print(larg_prod_grid(grid))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/012-highly_divisible_trian_num.py

@@ -0,0 +1,43 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+import math
+
+def find_div(n):
+    ''' find the divisor of a given n'''
+    set_div = {1, n}   
+    for i in range(2, int(math.sqrt(n))+ 1):
+        if not n % i:
+            set_div.add(i)
+            set_div.add(n//i) 
+    l1 = list(set_div)
+    return len(l1)
+    
+    
+def find_trian(l):
+    ''' find the lth trian number'''
+    return sum(range(1, l+1))
+
+
+def highly_divisible_trian_num(d):
+    thtriangle, n_div, count = 1, 0, 1
+    while n_div < d:
+        count += 1
+        thtriangle += count
+        n_div = find_div(thtriangle)
+    return (thtriangle, count)
+                
+    
+def main():
+    import time
+    start = time.time()   
+    assert(highly_divisible_trian_num(6) == (28, 7))
+    print(highly_divisible_trian_num(500))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/013-large_sum.py

@@ -0,0 +1,25 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def large_sum(filename):
+    sum_total, lines, numbers = 0, 0, 0
+    with open(filename) as file:
+        for line in file:
+            sum_total += int(line.strip('\n'))
+    return str(sum_total)[0:10]
+
+    
+def main():
+    import time
+    start = time.time() 
+      
+    filename = 'large_sum.dat'
+    print(large_sum(filename))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/014-long_collatz_seq.py

@@ -0,0 +1,43 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def find_coll_seq(n):
+    count = 1
+    while n > 1:
+        if n%2 == 0:
+            n = n//2
+        else:
+            n = 3*n +1
+        count += 1
+    return count
+
+
+def find_longest_chain(limit):
+    longest, number = 0, 0
+    start = 0
+    while start <= limit:
+        size_chain = find_coll_seq(start)
+        if size_chain > longest:
+            longest = size_chain
+            number = start
+        start += 1
+     
+    return (longest, number)
+
+
+
+    
+def main():
+    import time
+    start = time.time() 
+     
+    #print(find_longest_chain(13))
+    print(find_longest_chain(10**6))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/015-lattice_paths.py

@@ -0,0 +1,42 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def lattice_paths(squares):
+    gridsize = squares+1
+    grid = [[0 for i in range(gridsize)] for j in range(gridsize)]
+    row, col = 0, 0
+    
+    while col < gridsize:     
+        while row < gridsize: 
+        
+            if row == 0 and col == 0:
+                grid[row][col] = 1
+            
+            else:
+                if row == 0 and col != 0:
+                    grid[row][col] += grid[row][col-1]
+                elif row != 0 and col == 0:
+                    grid[row][col] += grid[row-1][col]  
+                else:
+                    grid[row][col] += grid[row][col-1] + grid[row-1][col] 
+            
+            row += 1 
+        row = 0
+        col += 1       
+    return grid[gridsize-1][gridsize-1]
+
+    
+def main():
+    import time
+    start = time.time() 
+    
+    assert(lattice_paths(2) == 6)
+    print(lattice_paths(20))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/016-power_digit_sum.py

@@ -0,0 +1,22 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+
+def power_digit_sum(n):
+    number = str(2**n)
+    sum_res = 0
+    for i in number:
+        sum_res += int(i)
+    return sum_res
+      
+    
+    
+def test_():
+    assert(power_digit_sum(15) == 26)
+    print(power_digit_sum(1000))
+    print('Tests Passed!')
+            
+if __name__ == '__main__':
+    test_()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/017-number_letter_counts.py

@@ -0,0 +1,63 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+
+
+def number_letter_counts(n):
+    dict_lett = build_dict(n)
+    sum_letter = 0
+    for item in dict_lett:
+        sum_letter += dict_lett[item]
+    return sum_letter 
+
+
+def build_dict(n):
+    lett_dict = {}
+    numbers = (x for x in range(1, n+1))
+    dec = ['one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine', 'ten', 'eleven', 'twelve', 'thirteen', 'fourteen', 'fifteen', 'sixteen', 'seventeen', 'eighteen', 'nineteen']
+    ties = ['twenty', 'thirty', 'forty', 'fifty', 'sixty', 'seventy', 'eighty', 'ninety']
+    
+    for number in numbers:
+        if 1 <= number < 20:
+            lett_dict[number] = len(dec[number-1])
+        elif 20 <= number < 100:
+            index_dec = number//10
+            index_num = number%10 
+            if index_num == 0:
+                lett_dict[number] = len(ties[index_dec-2])
+            else:
+                lett_dict[number] =  len(ties[index_dec-2])  +  len(dec[index_num-1])
+        elif 100 <= number < 1000:
+            index_hun = number//100
+            index_dec = number%100
+            if index_dec == 0:
+                lett_dict[number] = len(dec[index_hun-1]) + len('hundred')
+            else:
+                if 1 <= index_dec < 20:
+                    lett_dict[number] = len(dec[index_hun-1]) + len('hundred') + len('and') +  len(dec[index_dec-1])
+                elif  20 <= index_dec  < 100:
+                    index_dec2 = index_dec//10
+                    index_num = index_dec%10 
+                    if index_num == 0:
+                        lett_dict[number] = len(dec[index_hun-1]) + len('hundred') + len('and') +  len(ties[index_dec2-2])
+                    else:
+                        lett_dict[number] = len(dec[index_hun-1]) + len('hundred') + len('and') +  len(ties[index_dec2-2]) +  len(dec[index_num-1])
+        elif number == 1000:
+            lett_dict[number] = len('onethousand')
+            
+    return lett_dict
+                
+    
+def main():
+    import time
+    start = time.time() 
+      
+    assert(number_letter_counts(5) == 19)
+    print(number_letter_counts(1000))
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/018-max_path_sum.py

@@ -0,0 +1,55 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def max_path_sum(t):
+    root = t[0][0]
+    height, width, index, large_num = 1, 0, 0, 0
+    max_sum = root
+    heights = len(t[:])
+    
+    while height < heights:      
+        values_here = t[height][index:index+2]
+        if values_here[0] > values_here[1]:
+            large_num = values_here[0]
+        else:
+            large_num = values_here[1]
+            index += 1
+        max_sum += large_num
+        pivot = large_num
+        width, large_num = 0, 0
+        height += 1
+    
+    return max_sum
+
+def edit_input(filename):
+    output = []
+    with open(filename) as file:
+        for line in file:
+            line = line.rstrip('\n')
+            output.append(line.split(' '))
+    for i, l1 in enumerate(output):
+        for j, c in enumerate(output[i]):
+            output[i][j] = int(c)
+    return(output)
+
+
+
+def main():
+    import time
+    start = time.time() 
+    
+    filename = 'max_path_sum0.dat'
+    t1 = edit_input(filename)
+    print('Little pir: ',max_path_sum(t1))
+    
+    filename = 'max_path_sum.dat'
+    t2 = edit_input(filename)
+    print('Big pir: ', max_path_sum(t2))    
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/019-counting_sundays.py

@@ -0,0 +1,65 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+'''
+1 Jan 1900 was a Monday.
+Thirty days has September,
+April, June and November.
+All the rest have thirty-one,
+Saving February alone,
+Which has twenty-eight, rain or shine.
+And on leap years, twenty-nine.
+A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.
+How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
+'''
+
+
+def find_if_leap_year(y):
+    if (y%4 == 0 and y%100 != 0) or (y%400 == 0):
+        return True
+    return False
+
+   
+def counting_sundays():
+    ''' define variables '''
+    days_year = 7*31 + 4*30 + 28
+    count_sundays = 0  
+    days_week = 7 
+    dict_week = {0: 'mon', 1:'tue', 2:'wed', 3:'thu', 4:'fri', 5:'sat', 6:'sun'} 
+    
+    
+    ''' with info from 1900 find first day for 1901 '''
+    first_day = days_year%days_week  # not a leap year
+   
+    for y in range (1901, 2001):
+        leap_year = find_if_leap_year(y)
+        days_count = first_day
+               
+        for m in range(1, 13):
+            if days_count%7 == 6:
+                count_sundays += 1             
+            if m == 2:
+                if leap_year:
+                    days_count += 29
+                else: 
+                    days_count += 28
+            elif m == 4 or m == 6 or m == 9 or m == 11:
+                days_count += 30
+            else:
+                days_count += 31                  
+                 
+        if leap_year: first_day = (first_day +2)%days_week
+        else: first_day = (first_day +1)%days_week
+           
+    return count_sundays
+    
+    
+
+def main():
+    print(counting_sundays())
+    print('Tests Passed!')
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/020-factorial.py

@@ -0,0 +1,32 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def factorial(n):
+    prod = 1
+    for i in range(1,n):
+        prod *= i
+    return prod
+
+def find_sum(n):
+    sum_ = 0
+    fact = factorial(n)
+    number = str(fact)
+    for i in number:
+        sum_ += int(i)
+    return sum_
+
+
+def main():
+    import time
+    start = time.time() 
+    
+    assert(find_sum(10) == 27)  
+    print(find_sum(100))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/021-amicable_numbers.py

@@ -0,0 +1,44 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+'''
+Let d(n) be defined as the sum of proper divisors of n (numbers less than n which divide evenly into n).
+If d(a) = b and d(b) = a, where a  b, then a and b are an amicable pair and each of a and b are called amicable numbers.
+
+For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284. The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.
+
+Evaluate the sum of all the amicable numbers under 10000.
+'''
+
+def find_sum_proper_divisors(n):
+    sum_proper_div = 0
+    for i in range(1, n):
+        if n%i == 0:
+            sum_proper_div += i
+    return sum_proper_div
+
+
+def amicable_numbers(N):
+    sum_div_list = [find_sum_proper_divisors(i) for i in range(1, N+1)]
+    sum_amicable_numbers = 0
+    set_div = set()    
+    for a in range(1, N):
+        da = sum_div_list[a-1]
+        if da < N:
+            b = da
+            db = sum_div_list[b-1]
+            if a != b and db == a and a not in set_div and b not in set_div:
+                sum_amicable_numbers += a + b
+                set_div.add(a)
+                set_div.add(b)
+    return sum_amicable_numbers
+    
+
+def main():
+    print(amicable_numbers(10000))
+    print('Tests Passed!')
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/022-names_score.py

@@ -0,0 +1,33 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+
+def calculate_score(name, dict_letters):
+    sum_letters = 0
+    for letter in name:
+        sum_letters += dict_letters[letter]
+    return sum_letters 
+
+def names_score(filename):
+    dict_letters ={'A':1,'B':2,'C':3,'D':4,'E':5,'F':6,'G':7,'H':8,'I':9,'J':10,'K':11,'L':12,'M':13,'N':14,'O':15,'P':16,'Q':17,'R':18,'S':19, 'T':20,'U':21,'V':22,'W':23,'X':24,'Y':25,'Z':26}
+    total_score = 0
+    with open(filename) as file:
+        for line in file:
+            names = [name.strip('"') for name in line.split(',')]
+    names.sort()
+    for i, name in enumerate(names):
+        total_score += (i+1)* calculate_score(name, dict_letters)
+
+    return total_score
+
+
+    
+def main(): 
+    filename = 'names.txt'
+    print(names_score(filename))
+            
+            
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/023-non_abund_sums.py

@@ -0,0 +1,44 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def find_sum_proper_div(n):
+    sum_proper_div = 0
+    for i in range(1, n):
+        if n%i == 0:
+            sum_proper_div += i
+    return sum_proper_div     
+   
+   
+def find_all_abund(n):
+    sum_div_list = [find_sum_proper_div(i) for i in range(n)]
+    abu = set()
+    for i in range(n):
+        if i < sum_div_list[i]:
+            abu.add(i)
+    return abu
+      
+   
+def non_abund_sums(n):
+    abu = find_all_abund(n)  
+    sum_nom_abu = 0  
+    
+    for i in range(n):
+        if not any( (i-a in abu) for a in abu):
+            sum_nom_abu += i       
+       
+    return sum_nom_abu 
+    
+    
+def test_(): 
+    r = set([i for i in range(25)])
+    r_abu = {24}
+    r = r - r_abu
+    assert(non_abund_sums(25) == sum(r)) 
+    print(non_abund_sums(28123))
+    print('Tests Passed!')
+            
+            
+if __name__ == '__main__':
+    test_()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/024-lexico_per.py

@@ -0,0 +1,33 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def perm_item(elements):
+    if len(elements) <= 1:
+        yield elements  
+    else:
+        for (index, elmt) in enumerate(elements):
+            other_elmts = elements[:index]+elements[index+1:]
+            for permutation in perm_item(other_elmts): 
+                yield [elmt] + permutation
+
+
+def lex_perm(l1, n):
+    perm_list = list(perm_item(l1))
+    return sorted(perm_list)[n-1]
+
+
+def main():
+    import time
+    start = time.time() 
+    
+    l1 = [0,1,2,3,4,5,6,7,8,9]
+    n = 10**6
+    print(lex_perm(l1, n))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/025-100-digit-fib.py

@@ -0,0 +1,63 @@
+#!/usr/bin/python3
+# mari wahl @2014
+# marina.w4hl at gmail
+#
+
+'''
+The Fibonacci sequence is defined by the recurrence relation:
+ Fn = Fn−1 + Fn−2, where F1 = 1 and F2 = 1.
+ Hence the first 12 terms will be:
+
+F1 = 1
+F2 = 1
+F3 = 2
+F4 = 3
+F5 = 5
+F6 = 8
+F7 = 13
+F8 = 21
+F9 = 34
+F10 = 55
+F11 = 89
+F12 = 144
+The 12th term, F12, is the first term to contain three digits.
+
+What is the first term in the Fibonacci sequence to contain 1000 digits?
+Answer: 4782
+'''
+
+
+def fib(num=1, num_before=1):
+  found = False
+
+  num_before, num = num, num + num_before
+
+  if count_digits(num) == 1000: found = True
+
+  return num, num_before, found
+
+
+
+def count_digits(num):
+  num_str = str(num)
+  return len(num_str)
+
+
+
+def main():
+  found = False
+  num = 1
+  num_before = 1
+  count = 2
+
+  while not found:
+    num, num_before, found = fib(num, num_before)
+    count +=1
+
+  print(count)
+  print('Done!')
+
+if __name__ == '__main__':
+  main()
+
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/026-reciprocal-cycles.py

@@ -0,0 +1,40 @@
+#!/usr/bin/python3
+# mari wahl @2014
+# marina.w4hl at gmail
+
+
+'''
+A unit fraction contains 1 in the numerator. The decimal representation of the unit fractions with denominators 2 to 10 are given:
+
+1/2 =   0.5
+1/3 =   0.(3)
+1/4 =   0.25
+1/5 =   0.2
+1/6 =   0.1(6)
+1/7 =   0.(142857)
+1/8 =   0.125
+1/9 =   0.(1)
+1/10  =   0.1
+Where 0.1(6) means 0.166666..., and has a 1-digit recurring cycle. It can be seen that 1/7 has a 6-digit recurring cycle.
+
+Find the value of d < 1000 for which 1/d contains the longest recurring cycle in its decimal fraction part.
+
+Answer: 983
+'''
+
+
+def recurring_cycle(n, d):
+    for dd in range(1, d):
+        if 1 == 10**dd % d:
+            return dd
+    return 0
+
+def main():
+  n = 1
+  limit = 1000
+  longest = max(recurring_cycle(n, i) for i in range(2, limit+1))
+  print [i for i in range(2, limit+1) if recurring_cycle(n, i) == longest][0]
+
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/027-quad_primes.py

@@ -0,0 +1,50 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def quad_form(n, a, b):
+    return n**2 + a*n + b
+
+def isPrime(n):
+    n = abs(int(n))
+    if n < 2:
+        return False
+    if n == 2: 
+        return True    
+    if not n & 1: 
+        return False
+    for x in range(3, int(n**0.5)+1, 2):
+        if n % x == 0:
+            return False
+    return True
+
+def quad_primes(a, b):
+    count_max = 0
+    coef = ()
+    for aa in range(-a, a):
+        for bb in range(-b, b):  
+            n = 0 
+            while True: 
+                number = quad_form(n, aa, bb)
+                if isPrime(number):
+                    n += 1
+                else:
+                    if n > count_max:
+                        count_max = n
+                        coef = (aa, bb)
+                    break
+    return coef(0)*coef(1), coef
+   
+
+def main():
+    import time
+    start = time.time() 
+
+    print(quad_primes(1000, 1000))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/028-number_spiral.py

@@ -0,0 +1,39 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def number_spiral(spiral):
+    
+    
+    return rows, mid
+    
+def make_spiral(n):
+    spiral = []
+    row = rows//2
+    col = col//2
+    count = 1
+    while row < n:
+        while col < n:
+            spiral[col][row] = count
+            count += 1
+            if count%2 == 0:
+                col += 1
+            else:
+                row += 1
+        
+    return spiral
+
+def main():
+    import time
+    start = time.time() 
+    
+    n = 5
+    spiral = make_spiral(n)
+    print(number_spiral(spiral))# 101
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/029-dist_pow.py

@@ -0,0 +1,27 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def dist_pow(a1, a2, b1, b2):
+    set1 = set()
+    for a in range(a1, a2 + 1):
+        for b in range(b1, b2 + 1):
+            set1.add(a**b)          
+    return len(set1)
+
+    
+   
+
+def main():
+    import time
+    start = time.time() 
+
+    print(dist_pow(2, 5, 2, 5))    
+    print(dist_pow(2, 100, 2, 100))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/030-digit_fifth_pow.py

@@ -0,0 +1,30 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def digit_fifth_pow(n):
+    lnum = []   
+    for num in range(10**(2), 10**(n+2)):
+        sum_here = 0
+        num_str = str(num)
+        for i in num_str:
+            num_int = int(i)
+            num_int_pow = num_int**n
+            sum_here += num_int_pow 
+        if sum_here == num:
+            lnum.append(num)
+    return lnum, sum(lnum)
+   
+
+def main():
+    import time
+    start = time.time() 
+    
+    print(digit_fifth_pow(5))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/031-coin_sums.py

@@ -0,0 +1,28 @@
+#!/usr/bin/python3
+# mari wahl @2014
+# marina.w4hl at gmail
+'''
+In England the currency is made up of pound, £, and pence, p, and there are eight coins in general circulation:
+
+1p, 2p, 5p, 10p, 20p, 50p, £1 (100p) and £2 (200p).
+It is possible to make £2 in the following way:
+
+1×£1 + 1×50p + 2×20p + 1×5p + 1×2p + 3×1p
+How many different ways can £2 be made using any number of coins?
+'''
+
+
+
+
+def main():
+    import time
+    start = time.time()
+
+    print(digit_fifth_pow(5))
+
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))
+
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/032-pandigital.py

@@ -0,0 +1,51 @@
+#!/usr/bin/python
+
+
+__author__ = "Mari Wahl"
+__email__ = "marina.w4hl@gmail.com"
+
+'''
+We shall say that an n-digit number is pandigital if it makes use of all the digits 1 to n exactly once; for example, the 5-digit number, 15234, is 1 through 5 pandigital.
+The product 7254 is unusual, as the identity, 39 x 186 = 7254, containing multiplicand, multiplier, and product is 1 through 9 pandigital.
+Find the sum of all products whose multiplicand/multiplier/product identity can be written as a 1 through 9 pandigital.
+'''
+
+
+
+def isPandigitalString(string):
+    """ Check if string contains a pandigital number. """
+    digits = len(string)
+
+    if digits >= 10:
+        return False
+
+    for i in range(1,digits+1):
+        if str(i) not in string:
+            return False
+    return True
+
+
+
+def gives9PandigitalProduct(a, b):
+    numbers = str(a) + str(b) + str(a*b)
+    if len(numbers) != 9:
+        return False
+    return isPandigitalString(numbers)
+
+
+def main():
+    products = []
+
+    for a in range(0, 100000):
+        for b in range(a, 100000):
+            if len(str(a*b) + str(a) + str(b)) > 9:
+                break
+            if gives9PandigitalProduct(a, b):
+                products.append(a*b)
+                print("%i x %i = %i" % (a, b, a*b))
+
+    print(sum(set(products)))
+
+
+if __name__ == '__main__':
+    main()

book/ebook_src/real_interview_problems/other_resources/Project-Euler/035-circular_primes.py

@@ -0,0 +1,91 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def isPrime(n):
+    n = abs(int(n))
+    if n < 2:
+        return False
+    if n == 2:
+        return True
+    for x in range(2, int(n**0.5)+1):
+        if n%x == 0:
+            return False
+    return True
+
+
+def findPermutations(s):
+    res = []
+    if len(s) == 1:
+        res.append(s)
+    else:
+        for i, c in enumerate(s):
+            for perm in findPermutations(s[:i] + s[i+1:]):
+                res.append(c + perm)
+    return res
+
+    
+
+
+
+def isCircular(n):
+    n_str = str(n)
+    permutations = findPermutations(n_str)
+    for perm in permutations:
+        if not isPrime(perm):
+            return False
+    return True        
+    
+ 
+
+def generatePrimes(n):
+    if n == 2: return [2]
+    elif n < 2: return []
+    s = [i for i in range(3, n+1, 2)]
+    mroot = n ** 0.5
+    half = (n+1)//2 - 1
+    i, m = 0, 3
+    while m <= mroot:
+        if s[i]:
+            j = (m*m-3)//2
+            s[j] = 0
+            while j < half:
+                s[j] = 0
+                j += m
+        i = i+1
+        m = 2*i+3
+    return [2]+[x for x in s if x]
+
+
+def generate_n_Primes(n):
+    primes  = []
+    chkthis = 2
+    while len(primes) < n:
+        ptest    = [chkthis for i in primes if chkthis%i == 0]
+        primes  += [] if ptest else [chkthis]
+        chkthis += 1
+    return primes
+
+
+
+def circular_primes(n):
+    primes = generatePrimes(n)
+    count = 0
+    for prime in primes:
+        if isCircular(prime):
+            count += 1
+    return count
+    
+
+def main():
+    import time
+    start = time.time() 
+
+    print(circular_primes(1000000))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/046-gold_other.py

@@ -0,0 +1,64 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def isPrime(n):
+    n = abs(int(n))
+    if n < 2:
+        return False
+    if n == 2:
+        return True
+    if not n & 1:
+        return False
+    for x in range(3, int(n**0.5)+1, 2):
+        if n % x == 0:
+            return False
+    return True
+
+
+def generetePrimes(n):
+    if n == 2: return [2]
+    elif n < 2: return []
+    s = [i for i in range(3, n+1,2)]
+    mroot = n ** 0.5
+    half = (n+1)//2-1
+    i = 0
+    m = 3
+    while m <= mroot:
+        if s[i]:
+            j = (m*m - 3)//2
+            s[j] = 0
+            while j < half:
+                s[j] = 0
+                j += m
+        i = i+1
+        m = 2*i+3
+    return [2]+[x for x in s if x]
+
+
+def gold_other(n):
+    primes_for_n = generetePrimes(n)
+    numbers = {prime + 2*x**2 for prime in primes_for_n for x in range(1, int(n**0.5))}
+    conj = {x for x in range(3, n, 2) if not isPrime(x)}
+    
+    while True:
+        candidates = conj - numbers
+        if not candidates:
+            gold_other(2*n)
+        else:
+            return min(candidates)
+
+   
+
+def main():
+    import time
+    start = time.time() 
+
+    print(gold_other(10000))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/048-self_powers.py

@@ -0,0 +1,29 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def self_powers(power, digits):
+    sum_total = 0
+    for pow in range(1, power+1):
+        sum_total += pow**pow
+    sum_total_str = str(sum_total)
+    last_digits = ''
+    for i, c in enumerate(sum_total_str[-digits:]):
+        last_digits += c
+    return int(last_digits)
+
+
+def main():
+    import time
+    start = time.time() 
+    
+    
+    assert(self_powers(10, len('10405071317')) == 10405071317)
+    print(self_powers(1000, 10))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/065-100th-e-numerator.py

@@ -0,0 +1,43 @@
+#!/usr/bin/python
+
+__author__ = "Mari Wahl"
+__email__ = "marina.w4hl@gmail.com"
+
+'''
+e = [2; 1,2,1, 1,4,1, 1,6,1 , ... , 1,2k,1, ...].
+
+The first ten terms in the sequence of convergents for e are:
+
+2, 3, 8/3, 11/4, 19/7, 87/32, 106/39, 193/71, 1264/465, 1457/536, ...
+The sum of digits in the numerator of the 10th convergent is 1+4+5+7=17.
+
+Find the sum of digits in the numerator of the 100th convergent of the continued fraction for e.
+'''
+
+from itertools import islice
+
+def take(iterable, n):
+    #Make an iterator that returns selected elements from the iterable.
+    return list(islice(iterable, n))
+
+def e():
+    yield 2
+    k = 1
+    while True:
+        yield 1
+        yield 2*k
+        yield 1
+        k += 1
+
+def rationalize(frac):
+    if len(frac) == 0:
+        return (1, 0)
+    elif len(frac) == 1:
+        return (frac[0], 1)
+    else:
+        remainder = frac[1:len(frac)]
+        (num, denom) = rationalize(remainder)
+        return (frac[0] * num + denom, num)
+
+numerator = rationalize(take(e(), 100))[0]
+print sum(int(d) for d in str(numerator))

book/ebook_src/real_interview_problems/other_resources/Project-Euler/089-roman_numbers.py

@@ -0,0 +1,52 @@
+#!/usr/bin/python
+
+__author__ = "Mari Wahl"
+__email__ = "marina.w4hl@gmail.com"
+
+'''
+The rules for writing Roman numerals allow for many ways of writing each number (see About Roman Numerals...). However, there is always a "best" way of writing a particular number.
+
+For example, the following represent all of the legitimate ways of writing the number sixteen:
+
+IIIIIIIIIIIIIIII
+VIIIIIIIIIII
+VVIIIIII
+XIIIIII
+VVVI
+XVI
+
+The last example being considered the most efficient, as it uses the least number of numerals.
+
+The 11K text file, roman.txt (right click and 'Save Link/Target As...'), contains one thousand numbers written in valid, but not necessarily minimal, Roman numerals; that is, they are arranged in descending units and obey the subtractive pair rule (see About Roman Numerals... for the definitive rules for this problem).
+
+Find the number of characters saved by writing each of these in their minimal form.
+'''
+
+
+
+import os
+
+def subtractive(roman):
+    result = roman
+    replacements = [
+        ("VIIII", "IX"),
+        ("IIII", "IV"),
+        ("LXXXX", "XC"),
+        ("XXXX", "XL"),
+        ("DCCCC", "CM"),
+        ("CCCC", "CD"),
+    ]
+    for old, new in replacements:
+        result = result.replace(old, new)
+    return result
+
+
+if __name__ == '__main__':
+
+    current = 0
+    improved = 0
+    for line in open(os.path.join(os.path.dirname(__file__), 'roman.txt')):
+        roman = line.strip()
+        current += len(roman)
+        improved += len(subtractive(roman))
+    print current - improved

book/ebook_src/real_interview_problems/other_resources/Project-Euler/092-square_dig_chains.py

@@ -0,0 +1,38 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+def calculate_chain(n):
+    n_str = str(n)
+    while n_str != 1 or n_str != 89:
+        n_str = str(n_str)
+        sum_here = 0
+        for d in n_str:
+            sum_here += int(d)**2
+        n_str = sum_here
+        if n_str == 89:
+            return 1
+        if n_str == 1:
+            return 0
+        
+
+def square_dig_chains(n):
+    count = 0
+    for i in range(1, n+1):
+        count += calculate_chain(i)
+    return count
+    
+   
+
+def main():
+    import time
+    start = time.time() 
+
+    print(square_dig_chains(10**7))
+    
+    elapsed = (time.time() - start)
+    print('Tests Passed!\n It took %s seconds to run them.' % (elapsed))   
+                   
+if __name__ == '__main__':
+    main()
+

book/ebook_src/real_interview_problems/other_resources/Project-Euler/LICENSE

@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2014 Mari Wahl
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

book/ebook_src/real_interview_problems/other_resources/Project-Euler/README.md

@@ -0,0 +1,23 @@
+# 🍟 Project Euler Solutions 🍟
+
+Several of my solutions for the Euler project. For fun or profit :)
+
+Most of the exercises are written in Python, but I have some Java and Clojure too.
+
+Enjoy!
+
+![](http://projecteuler.net/profile/bytegirl.png)
+
+
+
+
+----
+
+
+## License
+
+When making a reference to my work, please use my [website](http://bt3gl.github.io/index.html).
+
+<a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by-sa/4.0/88x31.png" /></a><br />
+
+This work is licensed under a [Creative Commons Attribution-ShareAlike 4.0 International License](http://creativecommons.org/licenses/by-sa/4.0/).

book/ebook_src/real_interview_problems/other_resources/Project-Euler/larg_prod_grid.dat

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book/ebook_src/real_interview_problems/other_resources/Project-Euler/large_sum.dat

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book/ebook_src/real_interview_problems/other_resources/Project-Euler/max_path_sum.dat

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book/ebook_src/real_interview_problems/other_resources/Project-Euler/max_path_sum0.dat

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book/ebook_src/real_interview_problems/other_resources/Top-Coder/.gitignore

@@ -0,0 +1,54 @@
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+env/
+bin/
+build/
+develop-eggs/
+dist/
+eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+*.egg-info/
+.installed.cfg
+*.egg
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.coverage
+.cache
+nosetests.xml
+coverage.xml
+
+# Translations
+*.mo
+
+# Mr Developer
+.mr.developer.cfg
+.project
+.pydevproject
+
+# Rope
+.ropeproject
+
+# Django stuff:
+*.log
+*.pot
+
+# Sphinx documentation
+docs/_build/
+

book/ebook_src/real_interview_problems/other_resources/Top-Coder/2013/tco2013_round3_3b_div1.py

@@ -0,0 +1,70 @@
+#!/usr/bin/python3
+# mari von steinkirch @2013
+# steinkirch at gmail
+
+   
+                                
+def findToneDiff(tones):
+    tonesDiff = []
+    n = len(tones)    
+    for i, tone in enumerate(tones):
+        for j in range(i+1, len(tones)):  
+            sum_here = abs(tone - tones[j])
+            tonesDiff.append([sum_here, i, j])            
+    return sorted(tonesDiff)  
+     
+def findAllPossible(duration, tones, T):
+    tonesDiff = findToneDiff(tones)
+    sumsTone1 = [(song, i) for i, song in enumerate(duration) if song <= T]
+    sumsTone2 = []
+    for song in tonesDiff:
+        sum_here = song[0] + duration[song[1]] + duration[song[2]]
+        if sum_here <= T:
+            sumsTone2.append((sum_here, song[1], song[2], 2))
+    return sumsTone1, sumsTone2          
+            
+   
+def findAllPossibleNext(sumsTone, T, n_music):
+    sumsTone2 = []
+    for i, song1 in enumerate(sumsTone):
+        index1 = song1[1]
+        for j in range(i+1, len(sumsTone)):
+            song2 = sumsTone[j]
+            index2 = song2[1]
+            if index1 == index2:
+                sum_here = song1[0] + song2[0]
+                if sum_here < T:
+                    sumsTone2.append((sum_here, song2[1], song2[2], n_music))
+        
+                    
+    return sumsTone2
+            
+            
+def maxSongs(duration, tones, T):
+
+    if min(duration) >= T:
+            return 0
+               
+    sumsTone1, sumsTone = findAllPossible(duration, tones, T)
+    if not sumsTone:
+        return 1
+    
+    while sumsTone:
+        n_music = sumsTone[0][3]+1
+        sumsTone = findAllPossibleNext(sumsTone, T, n_music)    
+        if not sumsTone:
+            return n_music 
+
+
+   
+def tests_250():
+    print(maxSongs([3, 5, 4, 11], [2, 1, 3, 1], 17)) #3
+    print(maxSongs([9, 11, 13, 17], [2, 1, 3, 4], 20)) #1
+    print(maxSongs([100, 200, 300], [1,2,3], 99)) #0
+    print(maxSongs([87,21,20,73,97,57,12,80,86,97,98,85,41,12,89,15,41,17,68,37,21,1,9,65,4,67,38,91,46,82,7,98,21,70,99,41,21,65,11,1,8,12,77,62,52,69,56,33,98,97], [88,27,89,2,96,32,4,93,89,50,58,70,15,48,31,2,27,20,31,3,23,86,69,12,59,61,85,67,77,34,29,3,75,42,50,37,56,45,51,68,89,17,4,47,9,14,29,59,43,3], 212))
+
+
+                   
+if __name__ == '__main__':
+    tests_250()
+

book/ebook_src/real_interview_problems/other_resources/Top-Coder/README.md

@@ -0,0 +1,13 @@
+### 🍬 [Top Coder](Solutions) for Fun or Profit
+
+
+----
+
+
+## License
+
+When making a reference to my work, please use my [website](http://bt3gl.github.io/index.html).
+
+<a rel="license" href="http://creativecommons.org/licenses/by-sa/4.0/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by-sa/4.0/88x31.png" /></a><br />
+
+This work is licensed under a [Creative Commons Attribution-ShareAlike 4.0 International License](http://creativecommons.org/licenses/by-sa/4.0/).

book/ebook_src/real_interview_problems/other_resources/eudyptula-challenge-solutions/.gitignore

@@ -0,0 +1,30 @@
+# Compiled Object files
+*.slo
+*.lo
+*.o
+*.ko
+*.obj
+
+# Precompiled Headers
+*.gch
+*.pch
+
+# Compiled Dynamic libraries
+*.so
+*.dylib
+*.dll
+
+# Fortran module files
+*.mod
+*.smod
+
+# Compiled Static libraries
+*.lai
+*.la
+*.a
+*.lib
+
+# Executables
+*.exe
+*.out
+*.app

book/ebook_src/real_interview_problems/other_resources/eudyptula-challenge-solutions/LICENSE

@@ -0,0 +1,674 @@
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+
+  12. No Surrender of Others' Freedom.
+
+  If conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License.  If you cannot convey a
+covered work so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you may
+not convey it at all.  For example, if you agree to terms that obligate you
+to collect a royalty for further conveying from those to whom you convey
+the Program, the only way you could satisfy both those terms and this
+License would be to refrain entirely from conveying the Program.
+
+  13. Use with the GNU Affero General Public License.
+
+  Notwithstanding any other provision of this License, you have
+permission to link or combine any covered work with a work licensed
+under version 3 of the GNU Affero General Public License into a single
+combined work, and to convey the resulting work.  The terms of this
+License will continue to apply to the part which is the covered work,
+but the special requirements of the GNU Affero General Public License,
+section 13, concerning interaction through a network will apply to the
+combination as such.
+
+  14. Revised Versions of this License.
+
+  The Free Software Foundation may publish revised and/or new versions of
+the GNU General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+  Each version is given a distinguishing version number.  If the
+Program specifies that a certain numbered version of the GNU General
+Public License "or any later version" applies to it, you have the
+option of following the terms and conditions either of that numbered
+version or of any later version published by the Free Software
+Foundation.  If the Program does not specify a version number of the
+GNU General Public License, you may choose any version ever published
+by the Free Software Foundation.
+
+  If the Program specifies that a proxy can decide which future
+versions of the GNU General Public License can be used, that proxy's
+public statement of acceptance of a version permanently authorizes you
+to choose that version for the Program.
+
+  Later license versions may give you additional or different
+permissions.  However, no additional obligations are imposed on any
+author or copyright holder as a result of your choosing to follow a
+later version.
+
+  15. Disclaimer of Warranty.
+
+  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    {one line to give the program's name and a brief idea of what it does.}
+    Copyright (C) {year}  {name of author}
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    {project}  Copyright (C) {year}  {fullname}
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<http://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<http://www.gnu.org/philosophy/why-not-lgpl.html>.

book/ebook_src/real_interview_problems/other_resources/eudyptula-challenge-solutions/bt3/task_01/Makefile

@@ -0,0 +1,9 @@
+obj-m += eudyptula_1.o
+	KERNEL_VER ?= $(shell uname -r)
+	KERNEL_PATH ?= /lib/modules/$(KERNEL_VER)/build
+
+all:
+	make -C $(KERNEL_PATH) M=$(PWD) modules
+
+clean:
+	make -C $(KERNEL_PATH) M=$(PWD) clean

book/ebook_src/real_interview_problems/other_resources/eudyptula-challenge-solutions/bt3/task_01/eudyptula_1.c

@@ -0,0 +1,22 @@
+/*
+ * Eudyptula #1
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+
+int init_module(void)
+{
+	printk(KERN_DEBUG "Ola Mundo!\n");
+	return 0;
+}
+
+void cleanup_module(void)
+{
+	printk(KERN_DEBUG "Unloading exer 1! Goodbye!!!\n");
+}
+
+
+MODULE_LICENSE("GLP");
+MODULE_AUTHOR("7e1cf379bd3d");

book/ebook_src/real_interview_problems/other_resources/eudyptula-challenge-solutions/bt3/task_01/useful_commands

@@ -0,0 +1,5 @@
+make
+sudo insmod ./eudyptula_1.ko
+cat /proc/modules | grep eudyptula
+lsmod | grep eudyptula
+sudo rmmod eudyptula_1

book/ebook_src/real_interview_problems/other_resources/eudyptula-challenge-solutions/bt3/task_02/instructions.md

@@ -0,0 +1,42 @@
+1. Clone Linus’ repo and read Installing the kernel source:
+```
+$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
+```
+
+2. Generate .config and add CONFIG_LOCALVERSION_AUTO=y
+```
+$ make localmodconfig
+```
+
+3. Get an openssl header error, install lots of dev libraries
+```
+$ sudo apt-get install python-pip python-dev libffi-dev libssl-dev libxml2-dev libxslt1-dev libjpeg8-dev zlib1g-dev
+```
+
+4. Make! (It takes ~ 30 min)
+```
+$ make
+```
+
+5. Make module, install, add to grub 
+```
+$ make modules
+$ sudo make modules_install 
+$ sudo make install 
+$ update-grub
+```
+
+6. Reboot machine. For ubuntu: press shift to get grub menu 
+
+Profit!
+
+Some tips:
+* List of kernel addresses sorted in ascending order, from which it is simple to find the function that contains the offending address: 
+```
+$ nm vmlinux | sort | less 
+```
+
+Send
+```
+make && make modules && make modules_install && make install
+```

book/ebook_src/real_interview_problems/other_resources/eudyptula-challenge-solutions/bt3/task_02/readme.md

@@ -0,0 +1,34 @@
+This is Task 02 of the Eudyptula Challenge
+------------------------------------------
+
+Now that you have written your first kernel module, it's time to take
+off the training wheels and move on to building a custom kernel.  No
+more distro kernels for you.  For this task you must run your own
+kernel.  And use git!  Exciting, isn't it?  No?  Oh, ok...
+
+The tasks for this round are:
+  - Download Linus's latest git tree from git.kernel.org (you have to
+    figure out which one is his.  It's not that hard, just remember what
+    his last name is and you should be fine.)
+  - Build it, install it, and boot it.  You can use whatever kernel
+    configuration options you wish to use, but you must enable
+    CONFIG_LOCALVERSION_AUTO=y.
+  - Show proof of booting this kernel.  Bonus points if you do it on a
+    "real" machine, and not a virtual machine (virtual machines are
+    acceptable, but come on, real kernel developers don't mess around
+    with virtual machines, they are too slow.  Oh yeah, we aren't real
+    kernel developers just yet.  Well, I'm not anyway, I'm just a
+    script...)  Again, proof of running this kernel is up to you, I'm
+    sure you can do well.
+
+Hint, you should look into the 'make localmodconfig' option, and base
+your kernel configuration on a working distro kernel configuration.
+Don't sit there and answer all 1625 different kernel configuration
+options by hand, even I, a foolish script, know better than to do that!
+
+After doing this, don't throw away that kernel, git tree, and
+configuration file.  You'll be using it for later tasks.  A working
+kernel configuration file is a precious thing, all kernel developers
+have one they have grown and tended to over the years.  This is the
+start of a long journey with yours.  Don't discard it like was a broken
+umbrella, it deserves better than that.

book/ebook_src/real_interview_problems/other_resources/eudyptula-challenge-solutions/kiwiz/task_01/Makefile

@@ -0,0 +1,8 @@
+KERNEL_SRC ?= /lib/modules/$(shell uname -r)/build
+obj-m += task-01.o
+
+all:
+		make -C $(KERNEL_SRC) M=$(PWD) modules
+
+clean:
+		make -C $(KERNEL_SRC) M=$(PWD) clean

book/ebook_src/real_interview_problems/other_resources/eudyptula-challenge-solutions/kiwiz/task_01/task-01.c

@@ -0,0 +1,15 @@
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+
+static int __init setup(void) {
+    printk(KERN_DEBUG "Hello World!");
+
+    return 0;
+}
+
+static void __exit teardown(void) {
+}
+
+module_init(setup);
+module_exit(teardown);

book/ebook_src/real_interview_problems/other_resources/eudyptula-challenge-solutions/kiwiz/task_02/README.md

@@ -0,0 +1,6 @@
+Steps
+=====
+
+- `make`
+- `make modules_install`
+- `make install`

book/ebook_src/real_interview_problems/other_resources/eudyptula-challenge-solutions/kiwiz/task_03/README.md

@@ -0,0 +1,4 @@
+Steps
+=====
+
+- `git format-patch -o /tmp/ HEAD~`

book/ebook_src/real_interview_problems/other_resources/eudyptula-challenge-solutions/useful_scripts/sending_mutt.sh

@@ -0,0 +1 @@
+mutt -s [7e1cf379bd3d] Task 01 of the Eudyptula Challenge  little@eudyptula-challenge.org -a ~/Projects/eudyptula-challenge/task_01/eudyptula_1.c

book/ebook_src/real_interview_problems/other_resources/interview_cake/bitwise_stuff/clean_bit.py

@@ -0,0 +1,35 @@
+#!/usr/bin/python
+
+''' Clear a bit in a binary number.
+    Like the reverse of set bit:
+    1) first create a number filled of 1s,
+        with 0 at i (can create 0001000 and ~)
+    2) AND the number so it clears the ith bit
+'''
+
+
+
+def clear_bit(num, i):
+    mask = ~ (1 << i)   # -0b10001
+    return bin(num & mask)
+
+
+def clear_all_bits_from_i_to_0(num, i):
+    mask = ~ ( (1 << (i+1)) - 1)
+    return bin(num & mask)
+
+
+def clear_all_bits_from_most_sig_to_1(num, i):
+    mask =  ( 1 << i) -1
+    return bin(num & mask)
+
+
+if __name__ == '__main__':
+    num = int('10010000', 2)
+    print clear_bit(num, 4)   # '0b10000000'
+
+    num = int('10010011', 2)
+    print clear_all_bits_from_i_to_0(num, 2)  # '0b10010000'
+
+    num = int('1110011', 2)
+    print clear_all_bits_from_most_sig_to_1(num, 2)  #'0b11'

book/ebook_src/real_interview_problems/other_resources/interview_cake/bitwise_stuff/count_bits.py

@@ -0,0 +1,37 @@
+#!/usr/bin/python
+
+''' This method returns the number of bits that are necessary to change to convert two
+    numbers A and B:
+    1) XOR
+    2) count 1s
+'''
+
+def count_bits_swap2(a, b):
+    count = 0
+    m = a^b
+    while m:
+        count +=1
+        m = m & (m-1)
+    return count
+
+
+
+def count_bits_swap(a, b):
+    m = a^b
+    return count_1s(m)
+
+
+def count_1s(m):
+    count = 0
+    while m:
+        if m& 1 :
+            count +=1
+        m >>= 1
+    return count
+
+
+if __name__ == '__main__':
+    a = int('10010000', 2)
+    b = int('01011010', 2)
+    print count_bits_swap(a, b)  #4
+    print count_bits_swap2(a, b)  #4

book/ebook_src/real_interview_problems/other_resources/interview_cake/bitwise_stuff/get_bit.py

@@ -0,0 +1,20 @@
+#!/usr/bin/python
+''' Set a bit in a binary number:
+    1) Shifts 1 over by i bits
+    2) make an OR with the number, only the value at bit i will change and all the others bit
+    of the mask are zero so will not affect the num
+
+'''
+def set_bit(num, i):
+    mask = 1 << i
+    return bin( num | mask )
+
+
+if __name__ == '__main__':
+    num = int('0100100', 2)
+    print set_bit(num, 0)   #'0b100101'
+    print set_bit(num, 1)   #'0b100110'
+    print set_bit(num, 2)   # nothing change '0b100100'
+    print set_bit(num, 3)   #'0b101100'
+    print set_bit(num, 4) #'0b110100'
+    print set_bit(num, 5)     # nothing change '0b100100'

book/ebook_src/real_interview_problems/other_resources/interview_cake/bitwise_stuff/update_bit.py

@@ -0,0 +1,19 @@
+#!/usr/bin/python
+
+''' This method merges set bit and clean bit:
+    1) first clear the bit at i using a mask such as 1110111
+    2) then shift the intended value v by i bits
+    3) this will create a number with bit i to v and all other to 0
+    4) finally update the ith bit with or
+'''
+
+
+
+def  update_bit(num, i, v):
+    mask = ~ (1 << i)
+    return bin( (num & mask) | (v << i) )
+
+
+if __name__ == '__main__':
+    num = int('10010000', 2)
+    print update_bit(num, 2, 1)   # '0b10010100'

book/ebook_src/real_interview_problems/other_resources/interview_cake/data_structures/angry_bird.py

@@ -0,0 +1,37 @@
+#!/bin/python
+
+"""
+Each round, players receive a score between 0 and 100, which you use to rank them from highest to lowest. So far you're using an algorithm that sorts in O(n\lg{n})O(nlgn) time, but players are complaining that their rankings aren't updated fast enough. You need a faster sorting algorithm.
+
+Write a function that takes:
+
+a list of unsorted_scores
+the highest_possible_score in the game
+and returns a sorted list of scores in less than O(n\lg{n})O(nlgn) time.
+"""
+
+def sort_scores(unsorted_scores, highest_score):
+
+    score_counts = [0] * (highest_score+1)
+
+    for score in unsorted_scores:
+        score_counts[score] += 1
+
+    sorted_scores = []
+
+    for score in range(len(score_counts)-1, -1, -1):
+        count = score_counts[score]
+
+        for i in range(count):
+            sorted_scores.append(score)
+
+    return sorted_scores
+
+
+
+if __name__ == '__main__': 
+
+    unsorted_scores = [37, 89, 41, 65, 91, 53]
+    HIGHEST_POSSIBLE_SCORE = 100
+
+    print sort_scores(unsorted_scores, HIGHEST_POSSIBLE_SCORE)

book/ebook_src/real_interview_problems/other_resources/interview_cake/data_structures/file_system_hashing.py

@@ -0,0 +1,76 @@
+#!/bin/python
+
+"""
+Write a function that returns a list of all the duplicate files. 
+
+the first item is the duplicate file
+the second item is the original file
+For example:
+
+  [('/tmp/parker_is_dumb.mpg', '/home/parker/secret_puppy_dance.mpg'),
+ ('/home/trololol.mov', '/etc/apache2/httpd.conf')]
+You can assume each file was only duplicated once.
+"""
+
+import os
+import hashlib
+
+def find_duplicate_files(starting_directory):
+    files_seen_already = {}
+    stack = [starting_directory]
+
+    duplicates = []
+
+    while len(stack):
+        current_path = stack.pop()
+
+        if os.path.isdir(current_path):
+            for path in os.listdir(current_path):
+                full_path = os.path.join(current_path, path)
+                stack.append(full_path)
+
+        else:
+            file_hash = sample_hash_file(current_path)
+
+            current_last_edited_time = os.path.getmtime(current_path)
+
+            if file_hash in files_seen_already:
+                existing_last_edited_time, existing_path = files_seen_already[file_hash]
+                if current_last_edited_time > existing_last_edited_time:
+
+                    duplicates.append((current_path, existing_path))
+                else:
+
+                    duplicates.append((existing_path, current_path))
+                    files_seen_already[file_hash] = (current_last_edited_time, current_path)
+
+            else:
+                files_seen_already[file_hash] = (current_last_edited_time, current_path)
+
+    return duplicates
+
+
+def sample_hash_file(path):
+    num_bytes_to_read_per_sample = 4000
+    total_bytes = os.path.getsize(path)
+    hasher = hashlib.sha512()
+
+    with open(path, 'rb') as file:
+
+        if total_bytes < num_bytes_to_read_per_sample * 3:
+            hasher.update(file.read())
+        else:
+            num_bytes_between_samples = (
+                (total_bytes - num_bytes_to_read_per_sample * 3) / 2
+            )
+
+            for offset_multiplier in range(3):
+                start_of_sample = (
+                    offset_multiplier
+                    * (num_bytes_to_read_per_sample + num_bytes_between_samples)
+                )
+                file.seek(start_of_sample)
+                sample = file.read(num_bytes_to_read_per_sample)
+                hasher.update(sample)
+
+    return hasher.hexdigest()

book/ebook_src/real_interview_problems/other_resources/interview_cake/data_structures/inflight_entrain.py

@@ -0,0 +1,42 @@
+#!/bin/python
+
+"""
+Users on longer flights like to start a second movie right when their first one ends, 
+but they complain that the plane usually lands before they can see the ending. 
+So you're building a feature for choosing two movies whose total runtimes will equal the exact flight length.
+
+Write a function that takes an integer flight_length (in minutes) and a 
+list of integers movie_lengths (in minutes) and returns a boolean indicating 
+whether there are two numbers in movie_lengths whose sum equals flight_length.
+
+When building your function:
+
+Assume your users will watch exactly two movies
+Don't make your users watch the same movie twice
+Optimize for runtime over memory
+"""
+
+def is_there_two_movies(flight_length, movie_lengths):
+    movie_lengths_seen = set()
+
+    for first_movie_length in movie_lengths:
+        matching_second_movie_length = flight_length - first_movie_length
+        if matching_second_movie_length in movie_lengths_seen:
+            return True
+        movie_lengths_seen.add(first_movie_length)
+
+    return False
+
+
+
+if __name__ == '__main__':
+
+    flight_length = 10
+
+    movie_lengths = [2, 4, 7]
+    print(is_there_two_movies(flight_length, movie_lengths))
+    print("Should be True")
+
+    movie_lengths = [5, 6, 7, 8]
+    print(is_there_two_movies(flight_length, movie_lengths))
+    print("Should be False")

book/ebook_src/real_interview_problems/other_resources/interview_cake/math/apple_stocks.py

@@ -0,0 +1,27 @@
+#!/bin/python
+
+"""
+Grab Apple's stock prices and put them in a list called stock_prices, where:
+
+The indices are the time (in minutes) past trade opening time, which was 9:30am local time.
+The values are the price (in US dollars) of one share of Apple stock at that time.
+So if the stock cost $500 at 10:30am, that means stock_prices[60] = 500.
+
+Write an efficient function that takes stock_prices and returns the best profit I could have made from one purchase and one sale of one share.
+"""
+
+def apple_stock_profit(stock_prices):
+
+    min_s, max_s = max(stock_prices), 0
+
+    while stock_prices:
+        stock = stock_prices.pop()
+        min_s = min(min_s, stock)
+        max_s = max(max_s, stock)
+
+    return max_s - min_s
+
+
+stock_prices = [10, 7, 5, 8, 11, 9]
+print apple_stock_profit(stock_prices)
+print("Should return 6 (buying for $5 and selling for $11)")

book/ebook_src/real_interview_problems/other_resources/interview_cake/math/fib.py

@@ -0,0 +1,36 @@
+#!/bin/python
+
+"""
+Write a function fib() that takes an integer nn and returns the nnth Fibonacci number.
+"""
+
+# this is O(2^n)
+def fib(n):
+    if n in [1, 0]:
+        return n
+    return fib(n - 1) + fib(n - 2)
+    
+
+print fib(10)
+
+
+# this is O(n)
+def fib(n):
+    if n < 0:
+        raise ValueError('Index was negative. No such thing as a '
+                         'negative index in a series.')
+    elif n in [0, 1]:
+        return n
+
+    prev_prev = 0  # 0th fibonacci
+    prev = 1       # 1st fibonacci
+
+    for _ in range(n - 1):
+        current = prev + prev_prev
+        prev_prev = prev
+        prev = current
+
+    return current
+        
+
+print fib(10)

book/ebook_src/real_interview_problems/other_resources/interview_cake/math/find_dup.py

@@ -0,0 +1,38 @@
+#!/bin/python
+
+"""
+Find a duplicate
+We have a list of integers, where:
+The integers are in the range 1..n1..n
+The list has a length of n+1n+1
+It follows that our list has at least one integer which appears at least twice. But it may have several duplicates, and each duplicate may appear more than twice.
+
+Write a function which finds an integer that appears more than once in our list. (If there are multiple duplicates, you only need to find one of them.)
+"""
+
+def find_dups(num_list):
+    num_dict = {}
+    for n in num_list:
+        if n in num_dict.keys():
+            num_dict[n] += 1
+        else:
+            num_dict[n] = 1
+    
+    for k,v in num_dict.items():
+        if v > 1:
+            print "dup is {}".format(k)
+
+def find_dups_set(num_list):
+    
+    num_set = set()
+
+    for n in num_list:
+        if n in num_set:
+            print n
+        else:
+            num_set.add(n)
+
+
+num_list = [6,1,3,7,6,4,5,2,8,5,6,6,7]
+find_dups(num_list)
+find_dups_set(num_list)

book/ebook_src/real_interview_problems/other_resources/interview_cake/math/float_bin_num.py

@@ -0,0 +1,26 @@
+#!/usr/bin/python
+
+''' Given a real number between 0 and 1 (eg: 0.72), this method print the binary
+    representation. If the Number cannot be represented accurately in binary, with at
+    most 32 chars, print error:
+'''
+
+def get_float_rep(num):
+    if num >= 1 or num <= 0: return 'Error 1'
+    result = '.'
+    while num:
+        if len(result) >= 32: return 'Error 2', result
+        r = num*2
+        if r >= 1:
+            result += '1'
+            num = r - 1
+        else:
+            result += '0'
+            num = r
+    return result
+
+
+if __name__ == '__main__':
+    print get_float_rep(0.72) #('Error 2', '.1011100001010001111010111000010')
+    print get_float_rep(0.1) # ('Error 2', '.0001100110011001100110011001100')
+    print get_float_rep(0.5) #'.1'

book/ebook_src/real_interview_problems/other_resources/interview_cake/math/highest_product_3_int.py

@@ -0,0 +1,54 @@
+#!/bin/python
+
+"""
+Given a list of integers, find the highest product you can get from three of the integers.
+
+The input list_of_ints will always have at least three integers.
+"""
+
+def highest_num(list_of_ints):
+
+    if len(list_of_ints) == 3:
+        return list_of_ints[0]*list_of_ints[1]*list_of_ints[2]
+
+    sorted_list = sorted(list_of_ints)
+
+    return sorted_list[-3]*sorted_list[-2]*sorted_list[-1]
+
+
+def highest_product_of_3_On(list_of_ints):
+
+    highest = max(list_of_ints[0], list_of_ints[1])
+    lowest  = min(list_of_ints[0], list_of_ints[1])
+    highest_product_of_2 = list_of_ints[0] * list_of_ints[1]
+    lowest_product_of_2  = list_of_ints[0] * list_of_ints[1]
+
+    highest_product_of_3 = list_of_ints[0] * list_of_ints[1] * list_of_ints[2]
+
+    for i in range(2, len(list_of_ints)):
+        current = list_of_ints[i]
+
+        highest_product_of_3 = max(highest_product_of_3,
+                                   current * highest_product_of_2,
+                                   current * lowest_product_of_2)
+
+        highest_product_of_2 = max(highest_product_of_2,
+                                   current * highest,
+                                   current * lowest)
+
+        lowest_product_of_2 = min(lowest_product_of_2,
+                                  current * highest,
+                                  current * lowest)
+
+        highest = max(highest, current)
+
+        lowest = min(lowest, current)
+
+    return highest_product_of_3
+
+list_of_ints = [4, 2, 5, 6]
+print highest_num(list_of_ints)
+print "Should be 120"
+
+print highest_product_of_3_On(list_of_ints)
+print "Should be 120"

book/ebook_src/real_interview_problems/other_resources/interview_cake/math/in_place_shuffle.py

@@ -0,0 +1,33 @@
+#!/bin/python
+
+"""
+Write a function for doing an in-place shuffle of a list.
+
+The shuffle must be "uniform," meaning each item in the original list must have the same probability of ending up in each spot in the final list.
+
+Assume that you have a function get_random(floor, ceiling) for getting a random integer that is >= floor and <= ceiling.
+"""
+
+import random
+
+def get_random(floor, ceiling):
+    return random.randrange(floor, ceiling + 1)
+
+def shuffle(the_list):
+
+    if len(the_list) <= 1:
+        return the_list
+
+    last_index_in_the_list = len(the_list) - 1
+
+    for i in range(len(the_list) - 1):
+        random_choice_index = get_random(i,
+                                         last_index_in_the_list)
+        if random_choice_index != i:
+            the_list[i], the_list[random_choice_index] = \
+                the_list[random_choice_index], the_list[i]
+
+
+seed_list = [5, 2, 6, 2, 6]
+shuffle(seed_list)
+print seed_list

book/ebook_src/real_interview_problems/other_resources/interview_cake/math/product_every_int.py

@@ -0,0 +1,38 @@
+#!/bin/python
+
+"""
+You have a list of integers, and for each index you want to find the product of every integer except the integer at that index.
+
+Write a function get_products_of_all_ints_except_at_index() that takes a list of integers and returns a list of the products.
+
+For example, given:
+
+  [1, 7, 3, 4]
+
+your function would return:
+
+  [84, 12, 28, 21]
+ 
+by calculating:
+
+  [7 * 3 * 4,  1 * 3 * 4,  1 * 7 * 4,  1 * 7 * 3]
+ 
+Here's the catch: You can't use division in your solution!
+"""
+
+def get_products_of_all_ints_except_at_index(array):
+    prod_array = []
+
+    for i, num in enumerate(array):
+        prod = 1
+        for other_num in array[:i] + array[i+1:]:
+            prod *= other_num
+            
+        prod_array.append(prod)
+
+    return prod_array
+
+
+array = [1, 7, 3, 4]
+print get_products_of_all_ints_except_at_index(array)
+print "Should be [84, 12, 28, 21]"

book/ebook_src/real_interview_problems/other_resources/interview_cake/math/recursive_per.py

@@ -0,0 +1,32 @@
+#!/bin/python
+
+"""
+Write a recursive function for generating all permutations of an input string. Return them as a set.
+"""
+
+def get_permutations(string):
+
+    if len(string) < 2:
+        return set([string])
+
+    all_chars_except_last = string[:-1]
+    last_char = string[-1]
+
+    permutations_of_all_chars_except_last = get_permutations(all_chars_except_last)
+
+    permutations = set()
+    for permutation_of_all_chars_except_last in permutations_of_all_chars_except_last:
+        for position in range(len(all_chars_except_last) + 1):
+            permutation = (
+                permutation_of_all_chars_except_last[:position]
+                + last_char
+                + permutation_of_all_chars_except_last[position:]
+            )
+            permutations.add(permutation)
+
+    
+    return permutations
+
+
+str = "abcd"
+print get_permutations(str)

book/ebook_src/real_interview_problems/other_resources/interview_cake/sort_and_search/big_words.py

@@ -0,0 +1,70 @@
+#!/bin/python
+
+"""
+I want to learn some big words so people think I'm smart.
+
+I opened up a dictionary to a page in the middle and started flipping through, looking for words I didn't know. I put each word I didn't know at increasing indices in a huge list I created in memory. When I reached the end of the dictionary, I started from the beginning and did the same thing until I reached the page I started at.
+
+Now I have a list of words that are mostly alphabetical, except they start somewhere in the middle of the alphabet, reach the end, and then start from the beginning of the alphabet. In other words, this is an alphabetically ordered list that has been "rotated." For example:
+
+  words = [
+    'ptolemaic',
+    'retrograde',
+    'supplant',
+    'undulate',
+    'xenoepist',
+    'asymptote',  # <-- rotates here!
+    'babka',
+    'banoffee',
+    'engender',
+    'karpatka',
+    'othellolagkage',
+]
+
+Write a function for finding the index of the "rotation point," which is where I started working from the beginning of the dictionary. This list is huge (there are lots of words I don't know) so we want to be efficient here.
+"""
+
+def find_index(words):
+
+    for i, word in enumerate(words):
+        if word[0] > words[i+1][0]:
+            return i+1, words[i+1]
+
+    return "Not found"
+
+
+
+def find_index_bs(words):
+    first_word = words[0]
+    floor_index = 0
+    ceiling_index = len(words) - 1
+
+    while floor_index < ceiling_index:
+        guess_index = floor_index + ((ceiling_index - floor_index) / 2)
+
+        if words[guess_index] >= first_word:
+            floor_index = guess_index
+        else:
+            ceiling_index = guess_index
+
+        if floor_index + 1 == ceiling_index:
+            return ceiling_index
+
+
+words = [
+    'ptolemaic',
+    'retrograde',
+    'supplant',
+    'undulate',
+    'xenoepist',
+    'asymptote', 
+    'babka',
+    'banoffee',
+    'engender',
+    'karpatka',
+    'othellolagkage',
+]
+
+print find_index(words)
+print
+print find_index_bs(words)

book/ebook_src/real_interview_problems/other_resources/interview_cake/sort_and_search/binary_search.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python
+
+
+def binary_search(array, value):   
+    last, first = len(array), 0
+    
+    while first < last:
+        mid = (last - first)//2
+        item = array[mid]
+        
+        if item == value:
+            return True
+        
+        elif item < value:
+            last = mid
+        
+        else:
+            first = mid 
+    
+    return False
+
+def binary_search_rec(array, value, first=0, last=None):
+    last = last or len(array)
+    if len(array[first:last]) < 1:
+        return False
+    
+    mid = (last - first)//2
+    if array[mid] == value:
+        return True
+    elif array[mid] < value:
+        return binary_search_rec(array, value, first=first, last=mid)
+    else:
+        return binary_search_rec(array, value, first=mid, last=last)
+
+    
+array = [3, 4, 6, 7, 10, 11, 34, 67, 84]
+value = 6
+assert(binary_search(array, value) == True)   
+assert(binary_search_rec(array, value) == True)  
+value = 8
+assert(binary_search(array, value) == False)
+assert(binary_search_rec(array, value) == False)  
+array = [8]
+assert(binary_search(array, value) == True)
+assert(binary_search_rec(array, value) == True)  
+array = []
+assert(binary_search(array, value) == False)
+assert(binary_search_rec(array, value) == False)  

book/ebook_src/real_interview_problems/other_resources/interview_cake/sort_and_search/merge_sort.py

@@ -0,0 +1,37 @@
+ #!/usr/bin/env python
+
+def merge_sort(list_to_sort):
+    # Base case: lists with fewer than 2 elements are sorted
+    if len(list_to_sort) < 2:
+        return list_to_sort
+
+    # Step 1: divide the list in half
+    mid_index = len(list_to_sort) / 2
+    left  = list_to_sort[:mid_index]
+    right = list_to_sort[mid_index:]
+
+    # Step 2: sort each half
+    sorted_left  = merge_sort(left)
+    sorted_right = merge_sort(right)
+
+    # Step 3: merge the sorted halves
+    sorted_list = []
+    current_index_left = 0
+    current_index_right = 0
+
+    while len(sorted_list) < len(left) + len(right):
+        if ((current_index_left < len(left)) and
+                (current_index_right == len(right) or
+                 sorted_left[current_index_left] < sorted_right[current_index_right])):
+            sorted_list.append(sorted_left[current_index_left])
+            current_index_left += 1
+        else:
+            sorted_list.append(sorted_right[current_index_right])
+            current_index_right += 1
+    return sorted_list
+
+
+
+list_to_sort = [5, 3, 7, 12, 1, 0, 10]
+
+print merge_sort(list_to_sort)

book/ebook_src/real_interview_problems/other_resources/interview_cake/sort_and_search/merge_sorted_list.py

@@ -0,0 +1,52 @@
+#!/usr/bin/env python
+
+"""
+In order to win the prize for most cookies sold, my friend Alice and 
+# I are going to merge our Girl Scout Cookies orders and enter as one unit.
+# Each order is represented by an "order id" (an integer).
+We have our lists of orders sorted numerically already, in lists. 
+Write a function to merge our lists of orders into one sorted list.
+"""
+
+def merge_lists(my_list, alices_list):
+
+    result = []
+    index_alice_list = 0
+    index_my_list = 0
+
+    while index_alice_list < len(alices_list) and index_my_list < len(my_list):
+        if alices_list[index_alice_list] < my_list[index_my_list]:
+            result.append(alices_list[index_alice_list])
+            index_alice_list += 1
+        elif alices_list[index_alice_list] > my_list[index_my_list]:
+            result.append(my_list[index_my_list])
+            index_my_list += 1
+        else:
+            result.append(my_list[index_my_list])
+            result.append(alices_list[index_alice_list])
+            index_my_list += 1
+            index_alice_list += 1
+    
+    if index_alice_list < len(alices_list):
+        result.extend(alices_list[index_alice_list:])
+    
+    if index_my_list < len(my_list):
+        result.extend(my_list[index_my_list:])
+            
+    return result
+
+
+my_list     = [3, 4, 6, 10, 11, 15]
+alices_list = [1, 5, 8, 12, 14, 19]
+
+
+print merge_lists(my_list, alices_list)
+print "Must be [1, 3, 4, 5, 6, 8, 10, 11, 12, 14, 15, 19]"
+
+
+# Or just using Timsort
+def merge_sorted_lists(arr1, arr2):
+    return sorted(arr1 + arr2)
+
+print merge_sorted_lists(my_list, alices_list)
+print "Must be [1, 3, 4, 5, 6, 8, 10, 11, 12, 14, 15, 19]"

book/ebook_src/real_interview_problems/other_resources/interview_cake/strings/hical_str_manipulation.py

@@ -0,0 +1,51 @@
+#!/bin/python
+
+"""
+Build a calendar.
+
+A meeting is stored as a tuple of integers (start_time, end_time). 
+These integers represent the number of 30-minute blocks past 9:00am.
+
+For example:
+
+(2, 3)# Meeting from 10:00-10:30 am
+(6, 9)# Meeting from 12:00-1:30 pm
+
+Write a function merge_ranges() that takes a list of multiple meeting time ranges and returns a list of condensed ranges.
+
+For example, given:
+
+  [(0, 1), (3, 5), (4, 8), (10, 12), (9, 10)]
+ 
+your function would return:
+
+  [(0, 1), (3, 8), (9, 12)]
+ 
+Do not assume the meetings are in order. The meeting times are coming from multiple teams.
+
+Write a solution that's efficient even when we can't put a nice upper bound on the numbers representing our time ranges. 
+Here we've simplified our times down to the number of 30-minute slots past 9:00 am. 
+But we want the function to work even for very large numbers, like Unix timestamps. 
+In any case, the spirit of the challenge is to merge meetings where start_time and end_time don't have an upper bound.
+"""
+
+def merge_ranges(meetings):
+    
+    sorted_meetings = sorted(meetings)
+    merged_meetings = [sorted_meetings[0]]
+
+    for current_meeting_start, current_meeting_ending in sorted_meetings[1:]:
+        last_merged_meeting_start, last_merged_meeting_end = merged_meetings[-1]
+
+        if (current_meeting_start <= last_merged_meeting_end):
+            merged_meetings[-1] = (last_merged_meeting_start, max(last_merged_meeting_end, current_meeting_ending))
+        else:
+            merged_meetings.append((current_meeting_start, current_meeting_ending))
+
+    return merged_meetings
+
+if __name__ == '__main__':
+
+    meetings =  [(0, 1), (3, 5), (4, 8), (10, 12), (9, 10)]
+    print(merge_ranges(meetings))
+    print("Should return {}".format([(0, 1), (3, 8), (9, 12)]))

book/ebook_src/real_interview_problems/other_resources/interview_cake/strings/online_poker.py

@@ -0,0 +1,28 @@
+#!/bin/python
+
+"""
+Write a function to tell us if a full deck of cards shuffled_deck is a single riffle of two other halves half1 and half2.
+
+We'll represent a stack of cards as a list of integers in the range 1..521..52 (since there are 5252 distinct cards in a deck).
+Why do I care? A single riffle is not a completely random shuffle. If I'm right, I can make more informed bets and get rich and finally prove to my ex that I am not a "loser with an unhealthy cake obsession" (even though it's too late now because she let me go and she's never getting me back).
+"""
+
+def is_single_riffle(half1, half2, shuffled_deck,
+                     shuffled_deck_index=0, half1_index=0, half2_index=0):
+    if shuffled_deck_index == len(shuffled_deck):
+        return True
+
+    if ((half1_index < len(half1)) and
+            half1[half1_index] == shuffled_deck[shuffled_deck_index]):
+        half1_index += 1
+
+    elif ((half2_index < len(half2)) and
+            half2[half2_index] == shuffled_deck[shuffled_deck_index]):
+        half2_index += 1
+    else:
+        return False
+
+    shuffled_deck_index += 1
+    return is_single_riffle(
+        half1, half2, shuffled_deck, shuffled_deck_index,
+        half1_index, half2_index)