interview problems: trees

README.md

@@ -1,14 +1,12 @@
-Python and Algorithms & Data Structures
-=======================================
+# Python and Algorithms & Data Structures
 
 This repository contains a comprehensive study on Algorithms & Data Structures in Python, including an ["e-book" I wrote](http://mariwahl.us/docs/algorithms_in_python.pdf).
 
 ![](http://i.imgur.com/XruamX1.png)
 
 
-
-Source Code Structure
----------------------
+---
+## Source Code Structure
 
 
 src/
@@ -57,10 +55,12 @@ src/
 
     ├── sorting
 
+└── Extra Interview Problems
 
 
-Installation
-------------
+----
+## Installation
+
 The snippets are designed to be used individually. However, If you want  to install all fo the libraries in your [virtualenv](https://coderwall.com/p/8-aeka), do this:
 
 ```
@@ -68,22 +68,28 @@ $ pip install -r requirements.txt
 ```
 
 
+----
+## Further Learning
 
-Further Learning
------------------
-[Check out my lessons in machine learning.] (https://github.com/mariwahl/Machine-Learning-Lessons)
+### My Work:
+
+* [Check out my lessons in machine learning.] (https://github.com/mariwahl/Machine-Learning-Lessons)
 
 
 
-[Check out my lessons in numerical methods.](https://github.com/mariwahl/Numerical-Methods-for-Physics)
+* [Check out my lessons in numerical methods.](https://github.com/mariwahl/Numerical-Methods-for-Physics)
 
 
-[Neat Problems in Python and Flask](https://github.com/mariwahl/Neat-Problems-in-Python-and-Flask)
+* [Neat Problems in Python and Flask](https://github.com/mariwahl/Neat-Problems-in-Python-and-Flask)
+
+### Third Party:
+
+* [Interactive Python](http://interactivepython.org/)
 
 
+----
+## License
 
-License
-----------
 When making a reference to my work, please use my twitter handle [_b_t_3_](https://twitter.com/_b_t_3_) or 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 />

src/extra_interview_problems/glassdoor/2014/math_arrays_and_strings/max_subarray_stocks.py

@@ -1,31 +0,0 @@
-#!/usr/bin/env python
-
-__author__ = "bt3"
-
-
-
-def beating_stock(array):
-
-    imin = 0
-    i = 1
-    deal = [array[i] - array[imin], imin, i]
-
-    while i < len(array):
-
-        deal_here = array[i] - array[imin]
-        if deal_here > deal[0]:
-            deal = [deal_here, imin, i]
-
-        elif array[i] < array[imin]:
-            imin = i
-
-        i += 1
-
-    return deal[0], array[deal[1]], array[deal[2]]
-
-
-
-if __name__ == '__main__':
-    array = [7, 2, 3, 6, 5, 8, 5, 3, 4]
-    print(array)
-    print("Profit: %d, buying at %d, selling at %d." %(beating_stock(array)))

src/extra_interview_problems/glassdoor/2014/trees/binary_search_tree.py

@@ -1,72 +0,0 @@
-#!/usr/bin/python
-
-__author__ = "bt3"
-
-
-from binary_tree import NodeBT, BinaryTree
-
-
-class NodeBST(NodeBT):
-
-    def __init__(self, item=None, level=0):
-        self.item = item
-        self.level = level
-        self.left = None
-        self.right = None
-
-
-    def _addNextNode(self, value, level_here=1):
-        new_node = NodeBST(value, level_here)
-        if not self.item:
-            self.item = new_node
-        else:
-            if value > self.item:
-                self.right = self.right and self.right._addNextNode(value, level_here+1) or new_node
-            elif value < self.item:
-                self.left = self.left and self.left._addNextNode(value, level_here+1) or new_node
-            else:
-                print("BSTs do not support repeated items.")
-        return self # this is necessary!!!
-
-
-
-    def _searchForNode(self, value):
-        if self.item == value:
-            return self
-        elif self.left and value < self.item:
-                return self.left._searchForNode(value)
-        elif self.right and value > self.item:
-                return self.right._searchForNode(value)
-        else:
-            return False
-
-
-
-class BinarySearchTree(BinaryTree):
-
-    def __init__(self):
-        self.root = None
-
-    def addNode(self, value):
-        if not self.root:
-            self.root = NodeBST(value)
-        else:
-            self.root._addNextNode(value)
-
-
-
-
-if __name__ == '__main__':
-    bst = BinarySearchTree()
-    print "Adding nodes 1 to 10 in the tree..."
-    for i in range(1, 10):
-        bst.addNode(i)
-    print "Is 8 a leaf? ", bst.isLeaf(8)
-    print "Whats the level of node 8? ", bst.getNodeLevel(8)
-    print "Is node 10 a root? ", bst.isRoot(10)
-    print "Is node 1 a root? ", bst.isRoot(1)
-    print "Whats the tree height? ", bst.getHeight()
-    print "Is this tree BST? ", bst.isBST()
-    print "Is this tree balanced? ", bst.isBalanced()
-
-

src/extra_interview_problems/glassdoor/2014/trees/binary_tree.py

@@ -1,205 +0,0 @@
-#!/usr/bin/python
-
-__author__ = "bt3"
-
-
-
-''' Implementation of a binary tree and its properties. For example, the following bt:
-
-                               1                ---> level 0
-                        2             3         ---> level 1
-                  4         5                   ---> level 2
-              6      7                          ---> level 3
-            8   9                               ---> level 4
-
-    has the following properties:
-
-        - SIZE OR NUMBER OF NODES: n = 9
-        - NUMBER OF BRANCHES OR INTERNAL NODES: b = n-1 = 8
-        - VALUE OF ROOT = 1
-        - MAX_DEPTH OR HEIGHT: h = 4
-        - IS BALANCED? NO
-        - IS BST? NO
-'''
-
-
-class NodeBT(object):
-    def __init__(self, item=None, level=0):
-        self.item = item
-        self.level = level
-        self.left = None
-        self.right = None
-
-
-    def __repr__(self):
-        return '{}'.format(self.item)
-
-
-    def _addNextNode(self, value, level_here=1):
-        new_node = NodeBT(value, level_here)
-        if not self.item:
-            self.item = new_node
-        elif not self.left:
-            self.left = new_node
-        elif not self.right:
-            self.right = new_node
-        else:
-            self.left = self.left._addNextNode(value, level_here+1)
-        return self ## this is important, because the node return to the main
-
-
-    def _searchForNode(self, value):
-        if self.item == value:
-            return self
-        else:
-            found = None
-            if self.left:
-                found = self.left._searchForNode(value)
-            if self.right:
-                found =  found or self.right._searchForNode(value)
-            return found
-
-
-    def _isLeaf(self):
-        return not self.right and not self.left
-
-
-    def _getMaxHeight(self):
-        ''' Get the max height at the node, O(n)'''
-        levelr, levell = 0, 0
-        if self.right:
-            levelr = self.right._getMaxHeight() + 1
-        if self.left:
-            levell = self.left._getMaxHeight() + 1
-        return max(levelr, levell)
-
-
-    def _getMinHeight(self, level=0):
-        ''' Get the min height at the node, O(n)'''
-        levelr, levell = -1, -1
-        if self.right:
-            levelr = self.right._getMinHeight(level +1)
-        if self.left:
-            levell = self.left._getMinHeight(level +1)
-        return min(levelr, levell) + 1
-
-
-    def _isBalanced(self):
-        ''' Find whether the tree is balanced, by calculating heights first, O(n2) '''
-        if self._getMaxHeight() - self._getMinHeight() < 2:
-            return False
-        else:
-            if self._isLeaf():
-                return True
-            elif self.left and self.right:
-                return self.left._isBalanced() and   self.right._isBalanced()
-            elif not self.left and self.right:
-                return  self.right._isBalanced()
-            elif not self.right and self.left:
-                 return  self.left._isBalanced()
-
-    def _isBST(self, mintree=None, maxtree=None):
-        ''' Find whether the tree is a BST, inorder '''
-        if self.item:
-            if not mintree:
-                mintree = self.item
-            if not maxtree:
-                maxtree = self.item
-
-            if self._isLeaf():
-                return True
-            elif self.left:
-                if self.left.item < self.item and mintree > self.left.item:
-                    mintree = self.left.item
-                    return self.left._isBST(mintree, maxtree)
-                else:
-                    return False
-            elif self.right:
-                if self.right.item > self.item and maxtree < self.right.item:
-                    maxtree = self.right.item
-                    return self.right._isBST(mintree, maxtree)
-                else:
-                    return False
-        else:
-            print('Tree is empty')
-
-
-
-
-
-
-
-
-class BinaryTree(object):
-
-    def __init__(self):
-        self.root = None
-
-
-    def addNode(self, value):
-        if not self.root:
-            self.root = NodeBT(value)
-        else:
-            self.root._addNextNode(value)
-
-
-    def isLeaf(self, value):
-        node = self.root._searchForNode(value)
-        if node:
-            return node._isLeaf()
-        else:
-            print "Node not found."
-
-
-    def getNodeLevel(self, item):
-        node = self.root._searchForNode(item)
-        if node:
-            return node.level
-        else:
-            print('Node not found')
-
-
-    def isRoot(self, value):
-        return self.root.item == value
-
-
-    def getHeight(self):
-        return self.root._getMaxHeight()
-
-
-    def isBalanced(self):
-        return self.root._isBalanced()
-
-
-    def isBST(self):
-        return self.root._isBST()
-
-
-    def preorder(self):
-        current = self.root
-        nodes, stack = [], []
-        while stack or current:
-            if current:
-                nodes.append(current.item) # thats what change
-                stack.append(current)
-                current = current.left
-            else:
-                current = stack.pop()
-                current = current.right
-        return nodes
-
-
-
-if __name__ == '__main__':
-    bt = BinaryTree()
-    print "Adding nodes 1 to 10 in the tree..."
-    for i in range(1, 10):
-        bt.addNode(i)
-    print "Is 8 a leaf? ", bt.isLeaf(8)
-    print "Whats the level of node 8? ", bt.getNodeLevel(8)
-    print "Is node 10 a root? ", bt.isRoot(10)
-    print "Is node 1 a root? ", bt.isRoot(1)
-    print "Whats the tree height? ", bt.getHeight()
-    print "Is this tree BST? ", bt.isBST()
-    print "Is this tree balanced? ", bt.isBalanced()
-    print (bt.preorder())

src/extra_interview_problems/glassdoor/2014/trees/check_whether_bst.py

@@ -1,64 +0,0 @@
-__author__ = "bt3"
-
-
-""" need to keep track of min and max!!!"""
-
-from binary_tree import BinaryTree, NodeBT
-from binary_search_tree import BinarySearchTree, NodeBST
-
-## my solution
-
-def isBST(bt, mintree=None, maxtree=None):
-    if not bt.item:
-        return True
-
-    if not mintree:
-        mintree = bt.item
-
-    if not maxtree:
-        maxtree = bt.item
-
-    left, right = False, False
-
-    if bt.left:
-        if bt.left.item > bt.item and bt.left.item < mintree:
-            return False
-        else:
-            mintree = bt.left.item
-            left = isBST(bt.left, mintree, maxtree)
-    else:
-        left = True
-    if bt.right:
-        if bt.right.item < bt.item and bt.right.item > maxtree:
-            return False
-        else:
-            maxtree = bt.right.item
-            right = isBST(bt.right, mintree, maxtree)
-    else:
-        right = True
-
-    return  left and right
-
-
-
-
-
-
-
-
-
-if __name__ == '__main__':
-    bt = BinaryTree()
-    print "Adding nodes 1 to 10 in the tree..."
-    for i in range(1, 10):
-        bt.addNode(i)
-
-    print(isBST(bt.root))
-
-    bst = BinarySearchTree()
-    print "Adding nodes 1 to 10 in the tree..."
-    for i in range(1, 10):
-        bst.addNode(i)
-
-    print(isBST(bst.root))
-    print(bst.isBST())

src/extra_interview_problems/glassdoor/2014/trees/lowest_common_ancestor.py

@@ -1,47 +0,0 @@
-#!/usr/bin/python
-
-__author__ = "bt3"
-
-
-from binary_tree import BinaryTree
-
-
-def inorder(node, path=None):
-    if node:
-        path = path or []
-        path.append(node.item)
-        inorder(node.left, path)
-        inorder(node.right, path)
-    return path
-
-
-
-def lowest_commom_ancestor(node, node1, node2):
-    path = inorder(node.root)
-    i1, i2 = 0, 0
-    for i,n in enumerate(path):
-        if n == node1:
-            i1 = i
-        if n == node2:
-            i2 = i
-    return path[i1:i2+1]
-
-
-
-
-
-
-if __name__ == '__main__':
-    bt = BinaryTree()
-    l = [10, 6, 14, 3, 7, 11, 15]
-    for i in l:
-        bt.addNode(i)
-
-    print(l)
-    print(lowest_commom_ancestor(bt, 10, 6))
-    print(lowest_commom_ancestor(bt, 10, 14))
-    print(lowest_commom_ancestor(bt, 10, 3))
-    print(lowest_commom_ancestor(bt, 10, 7))
-    print(lowest_commom_ancestor(bt, 10, 11))
-    print(lowest_commom_ancestor(bt, 10, 15))
-

src/extra_interview_problems/glassdoor/2014/trees/transversal_BST_ancestor.py

@@ -1,44 +0,0 @@
-#!/usr/bin/python
-
-__author__ = "bt3"
-
-
-''' find the lowest ancestor in a BST '''
-
-from transversal_BST_recursively import BSTwithTransversalRecursively
-
-
-
-def find_ancestor(path, low_value, high_value):
-    while path:
-        current_value = path[0]
-        if current_value < low_value:
-            try:
-                path = path[2:]
-            except:
-                return current_value
-        elif current_value > high_value:
-            try:
-                path = path[1:]
-            except:
-                return current_value
-        elif low_value <= current_value <= high_value:
-            return current_value
-        else:
-            return None # this is probably never touched
-
-
-
-
-if __name__ == '__main__':
-    bst = BSTwithTransversalRecursively()
-    l = [10, 5, 15, 1, 6, 11, 50]
-    for i in l:
-        bst.addNode(i)
-    path = bst.preorder()
-    print("The path inorder: ", path)
-
-    print("The path between 1 and 6 is :", find_ancestor(path, 1, 6))
-    print("The path between 1 and 11 is: ", find_ancestor(path, 1, 11))
-    print("The path between 11 and 50 is: ", find_ancestor(path, 11, 50))
-    print("The path between 5 and 15 is: ", find_ancestor(path, 5, 15))

src/extra_interview_problems/glassdoor/2015/check_if_bst.py

@@ -1,56 +0,0 @@
-#!/usr/bin/env python
-
-__author__ = "bt3"
-
-
-'''
-Given a tree find out whether is a BST or not
-'''
-
-class Tree(object):
-    def __init__(self, value):
-        self.value = value
-        self.right = None
-        self.left = None
-
-def create_tree_bst():
-    tree = Tree(4)
-    tree.right = Tree(6)
-    tree.left = Tree(2)
-    tree.right.left = Tree(5)
-    tree.right.right = Tree(7)
-    tree.left.left = Tree(1)
-    tree.left.right = Tree(3)
-    return tree
-
-def create_tree_not_bst():
-    tree = Tree(4)
-    tree.right = Tree(6)
-    tree.left = Tree(2)
-    tree.right.left = Tree(5)
-    tree.right.right = Tree(7)
-    tree.left.left = Tree(3)
-    tree.left.right = Tree(1)
-    return tree
-
-
-INFINITY = float("infinity")
-NEG_INFINITY = float("-infinity")
-
-def isBST(tree, minVal=NEG_INFINITY, maxVal=INFINITY):
-    if not tree:
-        return True
-
-    if not minVal <= tree.value <= maxVal:
-        return False
-
-    return isBST(tree.left, minVal, tree.value) and \
-           isBST(tree.right, tree.value, maxVal)
-
-
-if __name__ == '__main__':
-    tree = create_tree_bst()
-    print isBST(tree)
-
-    tree = create_tree_not_bst()
-    print isBST(tree)

src/extra_interview_problems/math_arrays_and_strings/balance_symbols.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+'''
+Given a N different open and close braces in a string "( { [ } ] )".
+How do you check whether the string has matching braces.
+'''
+
+from collections import Counter
+def check_if_balance(string):
+    '''
+    >>> check_if_balance('{[[(])}]')
+    True
+    >>> check_if_balance('{[[()}]')
+    False
+    >>> check_if_balance('')
+    True
+    '''
+    table = Counter()
+    for i in string:
+
+        index = str(ord(i))[0]
+        if i in '{[(':
+            table[index] += 1
+
+        elif i in ')}]':
+            table[index] -= 1
+
+    for i in table.values():
+        if i !=-0:
+            return False
+    return True
+
+
+
+if __name__ == '__main__':
+    import doctest
+    doctest.testmod()
+

src/extra_interview_problems/math_arrays_and_strings/max_subarray_stocks.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+
+def beating_stock(array):
+
+    imin = 0
+
+    # first deal is just buying in the next day (1)
+    deal = [array[1] - array[imin], imin, 1]
+
+    for i, d in enumerate(array):
+
+        deal_here = d - array[imin]
+
+        if deal_here > deal[0]:
+            deal = [deal_here, imin, i]
+
+        elif d < array[imin]:
+            imin = i
+
+    return deal[0], array[deal[1]], array[deal[2]]
+
+if __name__ == '__main__':
+    array = [7, 2, 3, 6, 5, 8, 5, 3, 4]
+    deal = beating_stock(array)
+    print("Profit: %d, buying at %d, selling at %d." %(deal[0], deal[1], deal[2]))

src/extra_interview_problems/trees/binary_search_tree.py

@@ -0,0 +1,103 @@
+#!/usr/bin/python
+
+__author__ = "bt3"
+
+
+class Node(object):
+
+    def __init__(self, item=None,):
+
+        self.item = item
+        self.left = None
+        self.right = None
+
+    def __repr__(self):
+        return '{}'.format(self.item)
+
+
+    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 # this is necessary!!!
+
+
+    def _search(self, value):
+        if self.item == value:
+            return True # or self
+
+        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:
+            return self.left._printPreorder()
+
+        if self.right:
+            return self.right._printPreorder()
+
+
+
+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)
+
+
+
+if __name__ == '__main__':
+
+    bst = BST()
+    print "Adding nodes 1 to 10 in the tree..."
+    for i in range(1, 11):
+        bst.add(i)
+
+    print
+    print "Searching for nodes 16 and 6"
+    print bst.search(16)
+    print bst.search(6)
+
+    print
+    print "Printing preorder..."
+    bst.printPreorder()
+
+
+
+

src/extra_interview_problems/trees/binary_tree.py

@@ -0,0 +1,122 @@
+#!/usr/bin/python
+
+__author__ = "bt3"
+
+
+class Node(object):
+
+    def __init__(self, item=None,):
+
+        self.item = item
+        self.left = None
+        self.right = None
+
+    def __repr__(self):
+        return '{}'.format(self.item)
+
+
+    def _add(self, value):
+        new_node = Node(value)
+
+        if not self.item:
+            self.item = new_node
+        elif not self.left:
+            self.left = new_node
+        elif not self.right:
+            self.right = new_node
+        else:
+            self.left = self.left._add(value)
+        return self
+
+
+    def _search(self, value):
+        if self.item == value:
+            return True # or self
+
+        found = False # or False, thats diff from BST
+        if self.left:
+            found = self.left._search(value)
+
+        if self.right:
+            found =  found or self.right._search(value)
+
+        return found
+
+
+    def _isLeaf(self):
+        return not self.right and not self.left
+
+
+
+class BT(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):
+        current = self.root
+        nodes, stack = [], []
+        while stack or current:
+            if current:
+                nodes.append(current.item) # this is what change
+                stack.append(current)
+                current = current.left
+            else:
+                current = stack.pop()
+                current = current.right
+        print nodes
+
+
+    def printPostorder(self):
+        current = self.root
+        nodes, stack = [], []
+        while stack or current:
+
+            if current:
+                stack.append(current)
+                current = current.left
+            else:
+                current = stack.pop()
+                nodes.append(current.item) # this is what change
+                current = current.right
+        print nodes
+
+
+    def search(self, value):
+        if self.root:
+            return self.root._search(value)
+
+
+
+
+if __name__ == '__main__':
+
+    bt = BT()
+    print "Adding nodes 1 to 10 in the tree..."
+    for i in range(1, 11):
+        bt.add(i)
+
+    print
+    print "Searching for nodes 16 and 6"
+    print bt.search(16)
+    print bt.search(6)
+
+    print
+    print "Printing preorder..."
+    bt.printPreorder()
+
+    print
+    print "Printing postorder..."
+    bt.printPostorder()
+
+    print
+    print "Printing Inorder..."
+    bt.printInorder()

src/extra_interview_problems/trees/check_if_balanced.py

@@ -0,0 +1,30 @@
+__author__ = "bt3"
+
+
+from binary_search_tree import BST, Node
+from binary_tree import BT, Node
+
+
+
+def isBalanced(node, left=0, right=0):
+    if not node:
+        return (left - right) < 2
+
+    return isBalanced(node.left, left+1, right) and \
+        isBalanced(node.right, left, right+1)
+
+
+
+
+if __name__ == '__main__':
+    bt = BST()
+    for i in range(1, 10):
+        bt.add(i)
+
+    assert(isBalanced(bt.root) == True)
+
+    bt = BT()
+    for i in range(1, 10):
+        bt.add(i)
+
+    assert(isBalanced(bt.root) == False)

src/extra_interview_problems/trees/check_if_bst.py

@@ -0,0 +1,62 @@
+__author__ = "bt3"
+
+
+from binary_search_tree import BST, Node
+from binary_tree import BT, Node
+
+
+def isBST(node, min_node=float("-infinity"), maxVal=float("infinity")):
+    if not node:
+        return True
+
+    if not min_node <= node.item <= maxVal:
+        return False
+
+    return isBST(node.left, min_node, node.item) and \
+           isBST(node.right, node.item, maxVal)
+
+
+
+def isBST_other_method(node, max_node=None, min_node=None):
+
+    if not node:
+        return True
+
+    left, right =  True, True
+    min_node = min_node or float('inf')
+    max_node = max_node or -float('inf')
+
+    if node.left:
+        if node.left.item > node.item or node.left.item > max_node:
+            left = False
+        else:
+            max_node = node.item
+            left =  isBST(node.left, max_node, min_node)
+
+    if node.right:
+        if node.right.item < node.item or node.right.item < min_node:
+            rihjt =  False
+        else:
+            min_node = node.item
+            right =  isBST(node.right, max_node, min_node)
+
+    return left and right
+
+
+
+
+
+if __name__ == '__main__':
+    bt = BST()
+    for i in range(1, 10):
+        bt.add(i)
+
+    assert(isBST(bt.root) == True)
+
+    bt = BT()
+    for i in range(1, 10):
+        bt.add(i)
+
+    assert(isBST(bt.root) == False)
+
+