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   "metadata": {},
   "source": [
    "This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges)."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Solution Notebook"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Problem: Sort an array of strings so all anagrams are next to each other.\n",
    "\n",
    "* [Constraints](#Constraints)\n",
    "* [Test Cases](#Test-Cases)\n",
    "* [Algorithm](#Algorithm)\n",
    "* [Code](#Code)\n",
    "* [Unit Test](#Unit-Test)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Constraints\n",
    "\n",
    "* Are there any other sorting requirements other than the grouping of anagrams?\n",
    "    * No\n",
    "* Can we assume the inputs are valid?\n",
    "    * No\n",
    "* Can we assume this fits memory?\n",
    "    * Yes"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Test Cases\n",
    "\n",
    "* None -> Exception\n",
    "* [] -> []\n",
    "* General case\n",
    "    * Input: ['ram', 'act', 'arm', 'bat', 'cat', 'tab']\n",
    "    * Result: ['arm', 'ram', 'act', 'cat', 'bat', 'tab']"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Algorithm\n",
    "\n",
    "<pre>\n",
    "Input: ['ram', 'act', 'arm', 'bat', 'cat', 'tab']\n",
    "\n",
    "Sort the chars for each item:\n",
    "\n",
    "'ram' -> 'amr'\n",
    "'act' -> 'act'\n",
    "'arm' -> 'amr'\n",
    "'abt' -> 'bat'\n",
    "'cat' -> 'act'\n",
    "'abt' -> 'tab'\n",
    "\n",
    "Use a map of sorted chars to each item to group anagrams:\n",
    "\n",
    "{\n",
    "    'amr': ['ram', 'arm'], \n",
    "    'act': ['act', 'cat'], \n",
    "    'abt': ['bat', 'tab']\n",
    "}\n",
    "\n",
    "Result: ['arm', 'ram', 'act', 'cat', 'bat', 'tab']\n",
    "</pre>\n",
    "\n",
    "Complexity:\n",
    "* Time: O(k * n), due to the modified bucket sort\n",
    "* Space: O(n)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "from collections import OrderedDict\n",
    "\n",
    "\n",
    "class Anagram(object):\n",
    "\n",
    "    def group_anagrams(self, items):\n",
    "        if items is None:\n",
    "            raise TypeError('items cannot be None')\n",
    "        if not items:\n",
    "            return items\n",
    "        anagram_map = OrderedDict()\n",
    "        for item in items:\n",
    "            # Use a tuple, which is hashable and\n",
    "            # serves as the key in anagram_map\n",
    "            sorted_chars = tuple(sorted(item))\n",
    "            if sorted_chars in anagram_map:\n",
    "                anagram_map[sorted_chars].append(item)\n",
    "            else:\n",
    "                anagram_map[sorted_chars] = [item]\n",
    "        result = []\n",
    "        for value in anagram_map.values():\n",
    "            result.extend(value)\n",
    "        return result"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Overwriting test_anagrams.py\n"
     ]
    }
   ],
   "source": [
    "%%writefile test_anagrams.py\n",
    "import unittest\n",
    "\n",
    "\n",
    "class TestAnagrams(unittest.TestCase):\n",
    "\n",
    "    def test_group_anagrams(self):\n",
    "        anagram = Anagram()\n",
    "        self.assertRaises(TypeError, anagram.group_anagrams, None)\n",
    "        data = ['ram', 'act', 'arm', 'bat', 'cat', 'tab']\n",
    "        expected = ['ram', 'arm', 'act', 'cat', 'bat', 'tab']\n",
    "        self.assertEqual(anagram.group_anagrams(data), expected)\n",
    "\n",
    "        print('Success: test_group_anagrams')\n",
    "\n",
    "\n",
    "def main():\n",
    "    test = TestAnagrams()\n",
    "    test.test_group_anagrams()\n",
    "\n",
    "\n",
    "if __name__ == '__main__':\n",
    "    main()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Success: test_group_anagrams\n"
     ]
    }
   ],
   "source": [
    "%run -i test_anagrams.py"
   ]
  }
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