mirror of
https://github.com/donnemartin/interactive-coding-challenges.git
synced 2024-03-22 13:11:13 +08:00
330 lines
7.5 KiB
Python
330 lines
7.5 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 stack with push, pop, peek, and is_empty 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 we pop on an empty stack, do we 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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"### Push\n",
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"\n",
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"* Push to empty stack\n",
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"* Push to non-empty stack\n",
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"\n",
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"### Pop\n",
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"\n",
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"* Pop on empty stack\n",
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"* Pop on single element stack\n",
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"* Pop on multiple element stack\n",
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"\n",
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"### Peek\n",
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"\n",
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"* Peek on empty stack\n",
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"* Peek on one or more element stack\n",
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"\n",
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"### Is Empty\n",
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"\n",
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"* Is empty on empty stack\n",
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"* Is empty on one or more element stack"
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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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"### Push\n",
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"\n",
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"* Create new node with value\n",
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"* Set node's next to top\n",
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"* Set top 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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"### Pop\n",
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"\n",
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"* If stack is empty, return None\n",
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"* Else \n",
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" * Save top's value\n",
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" * Set top to top.next\n",
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" * Return 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)\n",
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"\n",
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"### Peek\n",
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"\n",
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"* If stack is empty, return None\n",
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"* Else return top's 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)\n",
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"\n",
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"### Is Empty\n",
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"* If peek has a value, return False\n",
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"* Else return True\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 stack.py\n"
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]
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}
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],
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"source": [
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"%%writefile stack.py\n",
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"class Node(object):\n",
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"\n",
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" def __init__(self, data, next=None):\n",
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" self.data = data\n",
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" self.next = next\n",
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"\n",
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"\n",
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"class Stack(object):\n",
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"\n",
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" def __init__(self, top=None):\n",
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" self.top = top\n",
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"\n",
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" def push(self, data):\n",
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" self.top = Node(data, self.top)\n",
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"\n",
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" def pop(self):\n",
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" if self.top is None:\n",
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" return None\n",
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" data = self.top.data\n",
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" self.top = self.top.next\n",
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" return data\n",
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"\n",
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" def peek(self):\n",
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" return self.top.data if self.top is not None else None\n",
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"\n",
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" def is_empty(self):\n",
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" return self.peek() is None"
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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 stack.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_stack.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_stack.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 TestStack(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: Empty stack')\n",
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" stack = Stack()\n",
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" assert_equal(stack.peek(), None)\n",
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" assert_equal(stack.pop(), None)\n",
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"\n",
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" print('Test: One element')\n",
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" top = Node(5)\n",
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" stack = Stack(top)\n",
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" assert_equal(stack.pop(), 5)\n",
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" assert_equal(stack.peek(), None)\n",
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"\n",
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" print('Test: More than one element')\n",
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" stack = Stack()\n",
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" stack.push(1)\n",
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" stack.push(2)\n",
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" stack.push(3)\n",
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" assert_equal(stack.pop(), 3)\n",
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" assert_equal(stack.peek(), 2)\n",
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" assert_equal(stack.pop(), 2)\n",
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" assert_equal(stack.peek(), 1)\n",
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" assert_equal(stack.is_empty(), False)\n",
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" assert_equal(stack.pop(), 1)\n",
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" assert_equal(stack.peek(), None)\n",
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" assert_equal(stack.is_empty(), True)\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 = TestStack()\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: Empty stack\n",
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"Test: One element\n",
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"Test: 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_stack.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-stacks\n",
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"<pre>\n",
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"5.1.1. Using Lists as Stacks\n",
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"The list methods make it very easy to use a list as a stack, where the last element added is the first element retrieved (“last-in, first-out”). To add an item to the top of the stack, use append(). To retrieve an item from the top of the stack, use pop() without an explicit index. For example:\n",
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"\n",
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">>> stack = [3, 4, 5]\n",
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">>> stack.append(6)\n",
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">>> stack.append(7)\n",
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">>> stack\n",
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"[3, 4, 5, 6, 7]\n",
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">>> stack.pop()\n",
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"7\n",
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">>> stack\n",
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"[3, 4, 5, 6]\n",
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">>> stack.pop()\n",
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"6\n",
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">>> stack.pop()\n",
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"5\n",
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">>> stack\n",
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"[3, 4]\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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