mirror of
https://github.com/donnemartin/interactive-coding-challenges
synced 2026-01-03 16:08:02 +00:00
312 lines
8.0 KiB
Python
312 lines
8.0 KiB
Python
{
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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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"<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).</i></small>"
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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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"# Solution Notebook"
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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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"## Problem: Implement a queue with enqueue and dequeue methods using a linked list.\n",
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"\n",
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"* [Constraints](#Constraints)\n",
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"* [Test Cases](#Test-Cases)\n",
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"* [Algorithm](#Algorithm)\n",
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"* [Code](#Code)\n",
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"* [Unit Test](#Unit-Test)\n",
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"* [Pythonic-Code](#Pythonic-Code)"
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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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"## Constraints\n",
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"\n",
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"* If there is one item in the list, do you expect the head and tail pointers to both point to it?\n",
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" * Yes\n",
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"* If there are no items on the list, do you expect the head and tail pointers to be None?\n",
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" * Yes\n",
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"* If you dequeue on an empty queue, does that return None?\n",
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" * Yes\n",
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"* Can we assume this fits memory?\n",
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" * Yes"
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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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"## Test Cases\n",
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"\n",
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"### Enqueue\n",
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"\n",
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"* Enqueue to an empty queue\n",
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"* Enqueue to a non-empty queue\n",
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"\n",
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"### Dequeue\n",
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"\n",
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"* Dequeue an empty queue -> None\n",
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"* Dequeue a queue with one element\n",
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"* Dequeue a queue with more than one element"
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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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"## Algorithm\n",
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"\n",
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"### Enqueue\n",
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"\n",
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"* If the list is empty, set head and tail to node\n",
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"* Else, set tail to node\n",
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"\n",
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"Complexity:\n",
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"* Time: O(1)\n",
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"* Space: O(1)\n",
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"\n",
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"### Dequeue\n",
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"\n",
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"* If the list is empty, return None\n",
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"* If the list has one node\n",
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" * Save the head node's value\n",
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" * Set head and tail to None\n",
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" * Return the saved value\n",
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"* Else\n",
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" * Save the head node's value\n",
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" * Set head to its next node\n",
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" * Return the saved value\n",
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"\n",
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"Complexity:\n",
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"* Time: O(1)\n",
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"* Space: O(1)"
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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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"## Code"
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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": 1,
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"metadata": {
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"collapsed": false
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},
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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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"Overwriting queue_list.py\n"
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]
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}
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],
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"source": [
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"%%writefile queue_list.py\n",
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"class Node(object):\n",
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"\n",
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" def __init__(self, data):\n",
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" self.data = data\n",
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" self.next = None\n",
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"\n",
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"\n",
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"class Queue(object):\n",
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"\n",
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" def __init__(self):\n",
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" self.head = None\n",
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" self.tail = None\n",
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"\n",
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" def enqueue(self, data):\n",
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" node = Node(data)\n",
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" # Empty list\n",
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" if self.head is None and self.tail is None:\n",
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" self.head = node\n",
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" self.tail = node\n",
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" else:\n",
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" self.tail.next = node\n",
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" self.tail = node\n",
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"\n",
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" def dequeue(self):\n",
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" # Empty list\n",
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" if self.head is None and self.tail is None:\n",
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" return None\n",
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" data = self.head.data\n",
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" # Remove only element from a one element list\n",
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" if self.head == self.tail:\n",
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" self.head = None\n",
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" self.tail = None\n",
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" else:\n",
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" self.head = self.head.next\n",
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" return data"
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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": 2,
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"metadata": {
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"collapsed": false
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},
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"outputs": [],
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"source": [
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"%run queue_list.py"
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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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"## Unit Test\n",
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"\n"
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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": 3,
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"metadata": {
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"collapsed": false
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},
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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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"Overwriting test_queue_list.py\n"
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]
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}
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],
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"source": [
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"%%writefile test_queue_list.py\n",
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"from nose.tools import assert_equal\n",
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"\n",
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"\n",
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"class TestQueue(object):\n",
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"\n",
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" # TODO: It would be better if we had unit tests for each\n",
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" # method in addition to the following end-to-end test\n",
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" def test_end_to_end(self):\n",
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" print('Test: Dequeue an empty queue')\n",
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" queue = Queue()\n",
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" assert_equal(queue.dequeue(), None)\n",
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"\n",
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" print('Test: Enqueue to an empty queue')\n",
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" queue.enqueue(1)\n",
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"\n",
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" print('Test: Dequeue a queue with one element')\n",
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" assert_equal(queue.dequeue(), 1)\n",
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"\n",
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" print('Test: Enqueue to a non-empty queue')\n",
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" queue.enqueue(2)\n",
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" queue.enqueue(3)\n",
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" queue.enqueue(4)\n",
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"\n",
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" print('Test: Dequeue a queue with more than one element')\n",
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" assert_equal(queue.dequeue(), 2)\n",
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" assert_equal(queue.dequeue(), 3)\n",
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" assert_equal(queue.dequeue(), 4)\n",
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"\n",
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" print('Success: test_end_to_end')\n",
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"\n",
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"\n",
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"def main():\n",
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" test = TestQueue()\n",
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" test.test_end_to_end()\n",
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"\n",
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"\n",
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"if __name__ == '__main__':\n",
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" main()"
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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": 4,
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"metadata": {
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"collapsed": false
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},
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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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"Test: Dequeue an empty queue\n",
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"Test: Enqueue to an empty queue\n",
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"Test: Dequeue a queue with one element\n",
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"Test: Enqueue to a non-empty queue\n",
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"Test: Dequeue a queue with more than one element\n",
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"Success: test_end_to_end\n"
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]
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}
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],
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"source": [
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"%run -i test_queue_list.py"
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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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"## Pythonic-Code"
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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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"Source: https://docs.python.org/2/tutorial/datastructures.html#using-lists-as-queues\n",
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"<pre>\n",
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"It is possible to use a list as a queue, where the first element added is the first element retrieved (“first-in, first-out”); however, lists are not efficient for this purpose. While appends and pops from the end of list are fast, doing inserts or pops from the beginning of a list is slow (because all of the other elements have to be shifted by one).\n",
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"\n",
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"To implement a queue, use collections.deque which was designed to have fast appends and pops from both ends. For example:\n",
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"\n",
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">>>\n",
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">>> from collections import deque\n",
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">>> queue = deque([\"Eric\", \"John\", \"Michael\"])\n",
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">>> queue.append(\"Terry\") # Terry arrives\n",
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">>> queue.append(\"Graham\") # Graham arrives\n",
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">>> queue.popleft() # The first to arrive now leaves\n",
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"'Eric'\n",
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">>> queue.popleft() # The second to arrive now leaves\n",
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"'John'\n",
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">>> queue # Remaining queue in order of arrival\n",
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"deque(['Michael', 'Terry', 'Graham'])\n",
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"</pre>"
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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": "3.5.0"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 0
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}
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