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https://github.com/donnemartin/interactive-coding-challenges
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Restructured packages.
This commit is contained in:
Donne Martin
193
stacks_queues/sort_stack/sort_stack.ipynb
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193
stacks_queues/sort_stack/sort_stack.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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"<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://bit.ly/code-notes).</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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"## Problem: Sort a stack. You can use another stack as a buffer.\n",
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"\n",
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"* [Constraints and Assumptions](#Constraints-and-Assumptions)\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)"
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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 and Assumptions\n",
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"\n",
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"*Problem statements are often intentionally ambiguous. Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
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"\n",
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"* When sorted, should the largest element be at the top or bottom?\n",
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" * Top\n",
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"* Can you have duplicate values like 5, 5?\n",
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" * Yes\n",
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"* Can we assume we already have a stack class that can be used for this problem?\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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"* Empty stack\n",
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"* One element stack\n",
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"* Two or more element stack (general case)\n",
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"* Already sorted 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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"* Our buffer will hold elements in reverse sorted order, smallest at the top\n",
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"* Store the current top element in a temp variable\n",
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"* While stack is not empty\n",
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" * While buffer is empty or buffer top is > than temp\n",
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" * Move buffer top to stack\n",
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" * Move temp to top of buffer\n",
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"* Return buffer\n",
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"\n",
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"Complexity:\n",
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"* Time: O(n^2)\n",
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"* Space: O(n)"
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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": true
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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": "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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"class MyStack(Stack):\n",
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" def sort(self):\n",
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" buff = MyStack()\n",
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" while not self.is_empty():\n",
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" temp = self.pop()\n",
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" while not buff.is_empty() and buff.peek() > temp:\n",
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" self.push(buff.pop())\n",
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" buff.push(temp)\n",
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" return buff"
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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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"*It is important to identify and run through general and edge cases from the [Test Cases](#Test-Cases) section by hand. You generally will not be asked to write a unit test like what is shown below.*"
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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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"Test: Empty stack\n",
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"Test: One element stack\n",
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"Test: Two or more element stack (general case)\n",
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"Success: test_sort_stack\n"
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]
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}
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],
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"source": [
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"from random import randint\n",
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"from nose.tools import assert_equal\n",
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"\n",
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"class Test(object):\n",
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" def get_sorted_stack(self, numbers):\n",
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" stack = MyStack()\n",
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" for x in numbers:\n",
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" stack.push(x)\n",
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" sorted_stack = stack.sort()\n",
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" return sorted_stack\n",
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"\n",
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" def test_sort_stack(self):\n",
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" print('Test: Empty stack')\n",
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" sorted_stack = self.get_sorted_stack([])\n",
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" assert_equal(sorted_stack.pop(), None)\n",
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"\n",
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" print('Test: One element stack')\n",
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" sorted_stack = self.get_sorted_stack([1])\n",
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" assert_equal(sorted_stack.pop(), 1)\n",
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"\n",
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" print('Test: Two or more element stack (general case)')\n",
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" num_items = 10\n",
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" numbers = [randint(0, 10) for x in xrange(num_items)]\n",
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" sorted_stack = self.get_sorted_stack(numbers)\n",
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" sorted_numbers = []\n",
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" for _ in xrange(num_items):\n",
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" sorted_numbers.append(sorted_stack.pop())\n",
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" assert_equal(sorted_numbers, sorted(numbers, reverse=True))\n",
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" \n",
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" print('Success: test_sort_stack')\n",
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"\n",
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"if __name__ == '__main__':\n",
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" test = Test()\n",
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" test.test_sort_stack()"
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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 2",
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"language": "python",
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"name": "python2"
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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": 2
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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": "ipython2",
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"version": "2.7.10"
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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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