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   "source": [
    "This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges)."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Challenge Notebook"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Problem: Implement merge sort.\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",
    "* Is a naive solution sufficient?\n",
    "    * Yes\n",
    "* Are duplicates allowed?\n",
    "    * Yes\n",
    "* Can we assume the input is valid?\n",
    "    * No\n",
    "* Can we assume this fits memory?\n",
    "    * Yes"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Test Cases\n",
    "\n",
    "* None -> Exception\n",
    "* Empty input -> []\n",
    "* One element -> [element]\n",
    "* Two or more elements\n",
    "* Left and right subarrays of different lengths"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Algorithm\n",
    "\n",
    "Refer to the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/sorting_searching/merge_sort/merge_sort_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": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "class MergeSort(object):\n",
    "\n",
    "    def sort(self, data):\n",
    "        # TODO: Implement me\n",
    "        pass"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test\n",
    "\n",
    "\n",
    "\n",
    "**The following unit test is expected to fail until you solve the challenge.**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# %load test_merge_sort.py\n",
    "import unittest\n",
    "\n",
    "\n",
    "class TestMergeSort(unittest.TestCase):\n",
    "\n",
    "    def test_merge_sort(self):\n",
    "        merge_sort = MergeSort()\n",
    "\n",
    "        print('None input')\n",
    "        self.assertRaises(TypeError, merge_sort.sort, None)\n",
    "\n",
    "        print('Empty input')\n",
    "        self.assertEqual(merge_sort.sort([]), [])\n",
    "\n",
    "        print('One element')\n",
    "        self.assertEqual(merge_sort.sort([5]), [5])\n",
    "\n",
    "        print('Two or more elements')\n",
    "        data = [5, 1, 7, 2, 6, -3, 5, 7, -1]\n",
    "        self.assertEqual(merge_sort.sort(data), sorted(data))\n",
    "\n",
    "        print('Success: test_merge_sort')\n",
    "\n",
    "\n",
    "def main():\n",
    "    test = TestMergeSort()\n",
    "    test.test_merge_sort()\n",
    "\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/sorting_searching/merge_sort/merge_sort_solution.ipynb) for a discussion on algorithms and code solutions."
   ]
  }
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