{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Problem: Sort a stack.  You can use another stack as a buffer.\n",
    "\n",
    "* [Clarifying Questions](#Clarifying-Questions)\n",
    "* [Test Cases](#Test-Cases)\n",
    "* [Algorithm](#Algorithm)\n",
    "* [Code](#Code)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Clarifying Questions\n",
    "\n",
    "* When sorted, should the largest element be at the top or bottom?\n",
    "    * Top\n",
    "* Can you have duplicate values, saw two 5s?\n",
    "    * Yes"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Test Cases\n",
    "\n",
    "* Empty stack\n",
    "* One element stack\n",
    "* Two or more element stack (general case)\n",
    "* Already sorted stack"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Algorithm\n",
    "\n",
    "* Our buffer will hold elements in reverse sorted order, smallest at the top\n",
    "* Store the current top element in a temp variable\n",
    "* While stack is not empty\n",
    "    * While buffer is empty or buffer top is > than temp\n",
    "        * Move buffer top to stack\n",
    "    * Move temp to top of buffer\n",
    "* Return buffer\n",
    "\n",
    "Complexity:\n",
    "* Time: O(n^2)\n",
    "* Space: O(n)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "%run stack.py"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "class MyStack(Stack):\n",
    "    def sort(self):\n",
    "        buff = MyStack()\n",
    "        while not self.is_empty():\n",
    "            temp = self.pop()\n",
    "            while not buff.is_empty() and buff.peek() > temp:\n",
    "                self.push(buff.pop())\n",
    "            buff.push(temp)\n",
    "        return buff"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "from random import randint\n",
    "\n",
    "def test_sort(num_items, stack=None):\n",
    "    if stack is None:\n",
    "        stack = MyStack()\n",
    "        for _ in xrange(0, num_items):\n",
    "            stack.push(randint(0, num_items))\n",
    "    sorted_stack = stack.sort()\n",
    "    for _ in xrange(0, num_items):\n",
    "        print(sorted_stack.pop())\n",
    "    return sorted_stack\n",
    "\n",
    "print('Empty stack')\n",
    "test_sort(0)\n",
    "print('One element stack')\n",
    "test_sort(1)\n",
    "print('Two or more element stack (general case)')\n",
    "sorted_stack = test_sort(5)"
   ]
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": "Python 2",
   "language": "python",
   "name": "python2"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 2
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython2",
   "version": "2.7.9"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 0
}