{
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  {
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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: Implement an algorithm to determine if a string has all unique characters\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 we assume this is case sensitive?\n",
    "    * Yes\n",
    "* Can you use additional data structures?\n",
    "    * Yes"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Test Cases\n",
    "\n",
    "* '' -> True\n",
    "* 'foo' -> False\n",
    "* 'bar' -> 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/unique_chars/unique_chars_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": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "def unique_chars(string):\n",
    "    from collections import defaultdict\n",
    "    \n",
    "    char_table = defaultdict(int)\n",
    "    for c in string:\n",
    "        if char_table[c] > 0:\n",
    "            return False\n",
    "        else:\n",
    "            char_table[c] = 1\n",
    "    return True"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**The following unit test is expected to fail until you solve the challenge.**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Success: test_unique_chars\n"
     ]
    }
   ],
   "source": [
    "# %load test_unique_chars.py\n",
    "from nose.tools import assert_equal\n",
    "\n",
    "\n",
    "class TestUniqueChars(object):\n",
    "\n",
    "  def test_unique_chars(self, func):\n",
    "        assert_equal(func(''), True)\n",
    "        assert_equal(func('foo'), False)\n",
    "        assert_equal(func('bar'), True)\n",
    "        print('Success: test_unique_chars')\n",
    "\n",
    "def main():\n",
    "    test = TestUniqueChars()\n",
    "    test.test_unique_chars(unique_chars)\n",
    "    try:\n",
    "        test.test_unique_chars(unique_chars_hash)\n",
    "        test.test_unique_chars(unique_chars_inplace)\n",
    "    except NameError:\n",
    "        # Alternate solutions are only defined\n",
    "        # in the solutions file\n",
    "        pass\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/unique_chars/unique_chars_solution.ipynb) for a discussion on algorithms and code solutions."
   ]
  }
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