From e5ad1f468be1d31df7200f375c53849ed4a744ae Mon Sep 17 00:00:00 2001
From: Donne Martin <donne.martin@gmail.com>
Date: Thu, 7 May 2015 19:59:28 -0400
Subject: [PATCH] Added notebook solving the following: Determine if a string
 s1 is a rotation of another string s2.

---
 arrays-strings/rotation.ipynb | 116 ++++++++++++++++++++++++++++++++++
 1 file changed, 116 insertions(+)
 create mode 100644 arrays-strings/rotation.ipynb

diff --git a/arrays-strings/rotation.ipynb b/arrays-strings/rotation.ipynb
new file mode 100644
index 0000000..19d05a6
--- /dev/null
+++ b/arrays-strings/rotation.ipynb
@@ -0,0 +1,116 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Determine if a string s1 is a rotation of another string s2.  Also write a function is_substring which you can only call once to determine whether a rotation occurs\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",
+    "* Is the string ASCII (extended)?  Or Unicode?\n",
+    "    * ASCII extended, which is 256 characters\n",
+    "* Can you use additional data structures?  \n",
+    "    * Yes\n",
+    "* Is this case sensitive?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* Any strings that differ in size results in False\n",
+    "* NULL, 'foo' -> False (any NULL results in False)\n",
+    "* ' ', 'foo' -> False\n",
+    "* ' ', ' ' -> True\n",
+    "* 'foobarbaz', 'barbazfoo' -> True"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "Using the following test case:\n",
+    "* s1 = 'barbazfoo'\n",
+    "* s2 = 'foobarbaz'\n",
+    "\n",
+    "We see that if we can use the given is_substring method if we take compare s2 with s1 + s1:\n",
+    "* s2 = 'foobarbaz'\n",
+    "* s3 = 'barbaz*foobarbaz*foo'\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(n)\n",
+    "* Space: O(2n) of additional space for s3, which reduces to O(n)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "def is_substring(s1, s2):\n",
+    "    return s1 in s2\n",
+    "\n",
+    "def is_rotation(s1, s2):\n",
+    "    if s1 is None or s2 is None:\n",
+    "        return False\n",
+    "    if len(s1) != len(s2):\n",
+    "        return False\n",
+    "    s3 = s1 + s1\n",
+    "    return is_substring(s2, s3)\n",
+    "\n",
+    "print(is_rotation('o', 'oo'))\n",
+    "print(is_rotation(None, 'foo'))\n",
+    "print(is_rotation('', 'foo'))\n",
+    "print(is_rotation('', ''))\n",
+    "print(is_rotation('foobarbaz', 'barbazfoo'))"
+   ]
+  }
+ ],
+ "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
+}