diff --git a/README.md b/README.md index 4fff186..90ac595 100644 --- a/README.md +++ b/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 diff --git a/sorting-searching/quick-sort.ipynb b/sorting-searching/quick-sort.ipynb new file mode 100644 index 0000000..06ea8ca --- /dev/null +++ b/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]])" + ] + } + ], + "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 +}