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   "metadata": {},
   "source": [
    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).</i></small>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Challenge Notebook"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Problem: Determine if a string s1 is a rotation of another string s2, by calling (only once) a function is_substring\n",
    "\n",
    "* [Constraints](#Constraints)\n",
    "* [Test Cases](#Test-Cases)\n",
    "* [Algorithm](#Algorithm)\n",
    "* [Code](#Code)\n",
    "* [Unit Test](#Unit-Test)\n",
    "* [Solution Notebook](#Solution-Notebook)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Constraints\n",
    "\n",
    "* Can you 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 -> False\n",
    "* None, 'foo' -> False (any None results in False)\n",
    "* ' ', 'foo' -> False\n",
    "* ' ', ' ' -> True\n",
    "* 'foobarbaz', 'barbazfoo' -> True"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Algorithm\n",
    "\n",
    "Refer to the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/arrays_strings/rotation/rotation_solution.ipynb).  If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "def is_substring(substr, s):\n",
    "    if len(s) < len(substr):\n",
    "        return False\n",
    "    elif len(substr) == len(s) and len(s) == 0:\n",
    "        return True\n",
    "    pos = 0\n",
    "    while pos < len(s):\n",
    "        so_far = 0\n",
    "        while so_far < len(substr):\n",
    "            if substr[so_far] != s[pos]:\n",
    "                pos = pos + 1\n",
    "                break\n",
    "            else:\n",
    "                pos = pos + 1\n",
    "                so_far = so_far + 1\n",
    "        if so_far == len(substr):\n",
    "            return True\n",
    "    return False\n",
    "\n",
    "def is_rotation(s1, s2):\n",
    "    if s1 is None or s2 is None:\n",
    "        return False\n",
    "    elif len(s1) != len(s2):\n",
    "        return False\n",
    "    else:\n",
    "        return is_substring(s2,s1+s1)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "\n",
    "\n",
    "**The following unit test is expected to fail until you solve the challenge.**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Success: test_rotation\n"
     ]
    }
   ],
   "source": [
    "# %load test_rotation.py\n",
    "from nose.tools import assert_equal\n",
    "\n",
    "\n",
    "class TestRotation(object):\n",
    "    \n",
    "    def test_rotation(self):\n",
    "        assert_equal(is_rotation('o', 'oo'), False)\n",
    "        assert_equal(is_rotation(None, 'foo'), False)\n",
    "        assert_equal(is_rotation('', 'foo'), False)\n",
    "        assert_equal(is_rotation('', ''), True)\n",
    "        assert_equal(is_rotation('foobarbaz', 'barbazfoo'), True)\n",
    "        print('Success: test_rotation')\n",
    "\n",
    "def main():\n",
    "    test = TestRotation()\n",
    "    test.test_rotation()\n",
    "\n",
    "if __name__ == '__main__':\n",
    "    main()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Solution Notebook\n",
    "\n",
    "Review the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/arrays_strings/rotation/rotation_solution.ipynb) for a discussion on algorithms and code solutions."
   ]
  }
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