Added notebook solving the following: Implement quick sort.

README.md

@@ -47,6 +47,7 @@ Most solutions are in Python.
 
 * [Implement selection sort](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/sorting-searching/selection-sort.ipynb#)
 * [Implement insertion sort](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/sorting-searching/insertion-sort.ipynb#)
+* [Implement quick sort](http://nbviewer.ipython.org/github/donnemartin/algorithms-data-structures/blob/master/sorting-searching/quick-sort.ipynb#)
 
 ## Hacker Rank
 

sorting-searching/quick-sort.ipynb

@@ -0,0 +1,158 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Implement quick sort.\n",
+    "\n",
+    "* [Clarifying Questions](#Clarifying-Questions)\n",
+    "* [Test Cases](#Test-Cases)\n",
+    "* [Algorithm](#Algorithm)\n",
+    "* [Code](#Code)\n",
+    "* [Pythonic-Code](#Pythonic-Code)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Clarifying Questions\n",
+    "\n",
+    "* Are you looking for a naiive quicksort (ie not in-place)?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* Empty input\n",
+    "* One element\n",
+    "* Two or more elements"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "* Set pivot to the middle element in the data\n",
+    "* For each element:\n",
+    "    * If current element is the pivot, continue\n",
+    "    * If the element is less than the pivot, add to left array\n",
+    "    * Else, add to right array\n",
+    "* Recursively apply quicksort to the left array\n",
+    "* Recursively apply quicksort to the right array\n",
+    "* Merge the left array + pivot + right array\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(n log(n)) average, best, O(n^2) worst\n",
+    "* Space: O(n), n extra space, n recursion depth"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "def quick_sort(data):\n",
+    "    if len(data) < 2:\n",
+    "        return data\n",
+    "    left = []\n",
+    "    right = []\n",
+    "    pivot_index = len(data) / 2\n",
+    "    pivot_value = data[pivot_index]\n",
+    "    for i in xrange(0, len(data)):\n",
+    "        if i == pivot_index:\n",
+    "            continue\n",
+    "        if data[i] < pivot_value:\n",
+    "            left.append(data[i])\n",
+    "        else:\n",
+    "            right.append(data[i])\n",
+    "    left = quick_sort(left)\n",
+    "    right = quick_sort(right)\n",
+    "    return left + [pivot_value] + right"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "print('Empty input')\n",
+    "data = []\n",
+    "#quick_sort(data)\n",
+    "print(data)\n",
+    "print('One element')\n",
+    "data = [5]\n",
+    "#quick_sort(data)\n",
+    "print(data)\n",
+    "print('Two or more elements')\n",
+    "data = [5, 1, 7, 2, 6, -3, 5, 7, -1]\n",
+    "print(quick_sort(data))"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Pythonic-Code\n",
+    "\n",
+    "From http://stackoverflow.com/questions/18262306/quick-sort-with-python"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "def quick_sort(arr): \n",
+    "     if len(arr) <= 1:\n",
+    "          return arr\n",
+    "     else:\n",
+    "          return qsort([x for x in arr[1:] if x<arr[0]]) + [arr[0]] + qsort([x for x in arr[1:] if x>=arr[0]])"
+   ]
+  }
+ ],
+ "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
+}