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Commit 7633ef8

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stacks, queues and dequeues implemented
1 parent aeea7ca commit 7633ef8

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2 files changed

+292
-7
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2 files changed

+292
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‎Arrays in Python.ipynb

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"print(unique_char_check(\"abcde\"))\n",
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"print(unique_char_check(\"abcdde\"))"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"source": []
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"metadata": {

‎Stacks, Queues, Deques.ipynb

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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Stacks\n",
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"Addition and deletion of items takes place through one end called the **top**. The enclosed end is called the **bottom**. An example is a stack of plates. New plates are placed at the top. Removal of plates also take place from the top. The item which is closer to the bottom is the one which had stayed in the stack the longest. The newer items stay close to the top. This is called **LIFO (Last In First Out)**.\n",
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"\n",
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"Insertion is called **push**. This means addition of item to the top. Deletion is called **pop**. This means removal of first item from the top. \n",
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"\n",
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"This data structure can be used for reversal of list."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 7,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"is empty True\n",
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"peeak me\n",
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"size 3\n",
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"is empty False\n",
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"is empty True\n"
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]
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}
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],
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"source": [
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"\"\"\"\n",
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"Stack class implementation\n",
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"\"\"\"\n",
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"\n",
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"class Stack(object):\n",
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" def __init__(self):\n",
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" self.items = []\n",
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" \n",
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" def is_empty(self):\n",
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" return self.items == []\n",
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" \n",
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" def push(self, item):\n",
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" self.items.append(item)\n",
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" \n",
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" def pop(self):\n",
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" return self.items.pop()\n",
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" \n",
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" def peek(self):\n",
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" return self.items[len(self.items) - 1]\n",
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" \n",
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" def size(self):T\n",
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" return len(self.items)\n",
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" \n",
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"s = Stack()\n",
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"print(\"is empty\", s.is_empty())\n",
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"s.push(1)\n",
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"s.push(\"me\")\n",
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"print(\"peeak\", s.peek())\n",
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"s.push(True)\n",
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"print(\"size\", s.size())\n",
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"print(\"is empty\", s.is_empty())\n",
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"s.pop()\n",
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"s.pop()\n",
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"s.pop()\n",
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"print(\"is empty\", s.is_empty())"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Queues\n",
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"It is an ordered collection of items where addition of new items happen at one end, called the **rear** and removal of existing items occur at the other end, called the **front**. This is called First In First Out **(FIFO)**. **Enqueue** is adding an item at the rear. **Dequeue** is removal of item from the front."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 9,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"size 0\n",
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"dequeue 1\n",
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"size 1\n"
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]
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}
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],
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"source": [
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"\"\"\"\n",
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"Queue class Implementation\n",
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"\"\"\"\n",
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"class Queue(object):\n",
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" def __init__(self):\n",
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" self.items = []\n",
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" \n",
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" def is_empty(self):\n",
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" return self.items == []\n",
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" \n",
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" def enqueue(self, item):\n",
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" self.items.insert(0, item)\n",
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" \n",
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" def dequeue(self):\n",
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" return self.items.pop()\n",
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" \n",
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" def size(self):\n",
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" return len(self.items)\n",
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" \n",
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"q = Queue()\n",
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"print(\"size\", q.size())\n",
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"q.enqueue(1)\n",
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"q.enqueue(2)\n",
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"print(\"dequeue\", q.dequeue())\n",
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"print(\"size\", q.size())"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Deque\n",
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"Double ended queue. It is similar to queue, except that it has an unrestricted nature of addition and removal of items. New items can be added to front or rear of deque. Same is for removal of item. Hence, it has characteristics of stack as well as queue."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 11,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"size 2\n",
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"Hello World\n",
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"size 0\n",
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"is empty? True\n"
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]
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}
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],
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"source": [
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"\"\"\"\n",
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"Deque class implementation\n",
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"\"\"\"\n",
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"\n",
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"class Deque(object):\n",
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" def __init__(self):\n",
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" self.items = []\n",
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" \n",
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" def is_empty(self):\n",
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" return self.items == []\n",
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" \n",
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" def add_front(self, item):\n",
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" self.items.append(item)\n",
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" \n",
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" def add_rear(self, item):\n",
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" self.items.insert(0, item)\n",
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" \n",
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" def remove_front(self):\n",
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" return self.items.pop()\n",
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" \n",
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" def remove_rear(self):\n",
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" return self.items.pop(0)\n",
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" \n",
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" def size(self):\n",
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" return len(self.items)\n",
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" \n",
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"d = Deque()\n",
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"d.add_front(\"Hello\")\n",
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"d.add_rear(\"World\")\n",
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"print(\"size\", d.size())\n",
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"print(d.remove_front(), d.remove_rear())\n",
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"print(\"size\", d.size())\n",
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"print(\"is empty?\", d.is_empty())"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Interview Questions"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 15,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"True\n",
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"False\n"
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]
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}
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],
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"source": [
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"\"\"\"\n",
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"Balanced Parentheses Check: has all three types of parantheses. Given a string of brackets only \n",
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"(no spaces or other characters), check if it is balanced\n",
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"\"\"\"\n",
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"\n",
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"def balance_check(s):\n",
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" if len(s)%2 != 0:\n",
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" return False\n",
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" opening = set('({[')\n",
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" matches = set([('(',')'),('{','}'),('[',']')])\n",
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" stack = []\n",
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" for i in s:\n",
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" if i in opening:\n",
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" stack.append(i)\n",
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" else:\n",
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" if len(stack) == 0:\n",
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" return False\n",
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" last_open = stack.pop()\n",
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" if (last_open, i) not in matches:\n",
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" return False\n",
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" return len(stack) == 0\n",
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"\n",
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"print(balance_check('[]'))\n",
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"print(balance_check('[[[({(})]]]'))"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 19,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"1\n",
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"2\n"
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]
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}
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],
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"source": [
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"\"\"\"\n",
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"Implement a Queue using 2 Stacks\n",
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"\"\"\"\n",
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"class Queue2Stacks(object):\n",
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" def __init__(self):\n",
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" self.in_stack = []\n",
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" self.out_stack = []\n",
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" \n",
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" def enqueue(self, item):\n",
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" self.in_stack.append(item)\n",
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" \n",
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" def dequeue(self):\n",
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" if not self.out_stack:\n",
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" while self.in_stack:\n",
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" self.out_stack.append(self.in_stack.pop())\n",
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" return self.out_stack.pop()\n",
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" \n",
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"q = Queue2Stacks()\n",
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"q.enqueue(1)\n",
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"q.enqueue(2)\n",
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"q.enqueue(3)\n",
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"print(q.dequeue())\n",
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"q.enqueue(4)\n",
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"print(q.dequeue())"
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.7.3"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 2
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}

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