Renamed top-level folders to use underscores instead of dashes.

arrays_strings/rotation/rotation.ipynb

@@ -0,0 +1,167 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<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>"
+   ]
+  },
+  {
+   "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",
+    "* [Constraints and Assumptions](#Constraints-and-Assumptions)\n",
+    "* [Test Cases](#Test-Cases)\n",
+    "* [Algorithm](#Algorithm)\n",
+    "* [Code](#Code)\n",
+    "* [Unit Test](#Unit-Test)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Constraints and Assumptions\n",
+    "\n",
+    "*Problem statements are often intentionally ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
+    "\n",
+    "* Can I assume the string is ASCII?\n",
+    "    * Yes\n",
+    "    * Note: Unicode strings could require special handling depending on your language\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": 1,
+   "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)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "*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.*"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Success: test_is_rotation\n"
+     ]
+    }
+   ],
+   "source": [
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "class Test(object):\n",
+    "    def test_is_rotation(self, func):\n",
+    "        assert_equal(func('o', 'oo'), False)\n",
+    "        assert_equal(func(None, 'foo'), False)\n",
+    "        assert_equal(func('', 'foo'), False)\n",
+    "        assert_equal(func('', ''), True)\n",
+    "        assert_equal(func('foobarbaz', 'barbazfoo'), True)\n",
+    "        print('Success: test_is_rotation')\n",
+    "\n",
+    "if __name__ == '__main__':\n",
+    "    test = Test()\n",
+    "    test.test_is_rotation(is_rotation)"
+   ]
+  }
+ ],
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