From 8aca11b1714652890e89b09b857c6b99c014f389 Mon Sep 17 00:00:00 2001
From: bt3 <marina@yelp.com>
Date: Sun, 25 Oct 2015 20:15:48 -0700
Subject: [PATCH] warmup, preparing to give interviews

---
 short_phone_interview_problems/balanced.py |  22 +++
 short_phone_interview_problems/bst.py      | 165 +++++++++++++++++++++
 short_phone_interview_problems/queue.py    |  47 ++++++
 short_phone_interview_problems/stack.py    |  40 +++++
 4 files changed, 274 insertions(+)
 create mode 100644 short_phone_interview_problems/balanced.py
 create mode 100644 short_phone_interview_problems/bst.py
 create mode 100644 short_phone_interview_problems/queue.py
 create mode 100644 short_phone_interview_problems/stack.py

diff --git a/short_phone_interview_problems/balanced.py b/short_phone_interview_problems/balanced.py
new file mode 100644
index 0000000..760316d
--- /dev/null
+++ b/short_phone_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('(()'))
\ No newline at end of file
diff --git a/short_phone_interview_problems/bst.py b/short_phone_interview_problems/bst.py
new file mode 100644
index 0000000..f908e10
--- /dev/null
+++ b/short_phone_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)
\ No newline at end of file
diff --git a/short_phone_interview_problems/queue.py b/short_phone_interview_problems/queue.py
new file mode 100644
index 0000000..c2ec415
--- /dev/null
+++ b/short_phone_interview_problems/queue.py
@@ -0,0 +1,47 @@
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+class Queue(object):
+    def __init__(self):
+        self.enq = []
+        self.deq = []
+
+    def enqueue(self, item):
+        return self.enq.append(item)
+
+    def deque(self):
+        if not self.deq:
+            while self.enq:
+                self.deq.append(self.enq.pop())
+        return self.deq.pop()
+
+    def peak(self):
+        if not self.deq:
+            while self.enq:
+                self.deq.append(self.enq.pop())
+        if self.deq:
+            return self.deq[-1]
+
+    def size(self):
+        return len(self.enq) + len(self.deq)
+
+    def isempty(self):
+        return not (self.enq + self.deq)
+
+    
+if __name__ == '__main__':
+    q = Queue()
+    for i in range(1,11):
+        q.enqueue(i)
+    print 'Size:',  q.size()
+    print 'Is empty?', q.isempty()
+    print 'Peak: ', q.peak()
+    print
+    print 'Dequeuing...'
+    for i in range(10):
+        print q.deque()
+    print 'Size:',  q.size()
+    print 'Is empty?', q.isempty()
+    print 'Peak: ', q.peak()
\ No newline at end of file
diff --git a/short_phone_interview_problems/stack.py b/short_phone_interview_problems/stack.py
new file mode 100644
index 0000000..07e9e06
--- /dev/null
+++ b/short_phone_interview_problems/stack.py
@@ -0,0 +1,40 @@
+
+#!/usr/bin/env python
+
+__author__ = "bt3"
+
+
+class Stack(object):
+    def __init__(self):
+        self.content = []
+
+    def push(self, value):
+        self.content.append(value)
+
+    def pop(self):
+        if self.content:
+            return self.content.pop()
+        else:
+            return 'Empty List. '
+
+    def size(self):
+        return len(self.content)
+
+    def isEmpty(self):
+        return not bool(self.content)
+
+    def peek(self):
+        if self.content:
+            return self.content[-1]
+        else:
+            print('Stack is empty.')
+
+
+
+if __name__ == '__main__':
+    q = Stack()
+
+    for i in range(10):
+        q.push(i)
+    for i in range(11):
+        print q.pop()
\ No newline at end of file