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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": [
    "# Challenge Notebook"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Problem: Find the in-order successor of a given node in a binary search tree.\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",
    "* If there is no successor, do we return None?\n",
    "    * Yes\n",
    "* Can we assume we already have a Node class that keeps track of parents?\n",
    "    * Yes"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Test Cases\n",
    "\n",
    "<pre>\n",
    "          _5_\n",
    "        /     \\\n",
    "       3       8\n",
    "      / \\    /   \\\n",
    "     2   4  6    12\n",
    "    /        \\   / \\\n",
    "   1          7 10  15\n",
    "               /\n",
    "              9\n",
    "\n",
    "In: 4  Out: 5\n",
    "In: 5  Out: 6\n",
    "In: 8  Out: 9\n",
    "In: 15 Out: None\n",
    "</pre>"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Algorithm\n",
    "\n",
    "Refer to the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/bst_successor/bst_successor_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": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "%run ../bst/bst.py\n",
    "%load ../bst/bst.py"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "def bst_successor(node):\n",
    "    # TODO: Implement me\n",
    "    pass"
   ]
  },
  {
   "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": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "# %load test_bst_successor.py\n",
    "from nose.tools import assert_equal\n",
    "\n",
    "\n",
    "class TestBstSuccessor(object):\n",
    "\n",
    "    def test_bst_successor(self):\n",
    "        nodes = {}\n",
    "        node = Node(5)\n",
    "        nodes[5] = node\n",
    "        nodes[3] = insert(node, 3)\n",
    "        nodes[8] = insert(node, 8)\n",
    "        nodes[2] = insert(node, 2)\n",
    "        nodes[4] = insert(node, 4)\n",
    "        nodes[6] = insert(node, 6)\n",
    "        nodes[12] = insert(node, 12)\n",
    "        nodes[1] = insert(node, 1)\n",
    "        nodes[7] = insert(node, 7)\n",
    "        nodes[10] = insert(node, 10)\n",
    "        nodes[15] = insert(node, 15)\n",
    "        nodes[9] = insert(node, 9)\n",
    "\n",
    "        assert_equal(bst_successor(nodes[4]), 5)\n",
    "        assert_equal(bst_successor(nodes[5]), 6)\n",
    "        assert_equal(bst_successor(nodes[8]), 9)\n",
    "        assert_equal(bst_successor(nodes[15]), None)\n",
    "\n",
    "        print('Success: test_bst_successor')\n",
    "\n",
    "\n",
    "def main():\n",
    "    test = TestBstSuccessor()\n",
    "    test.test_bst_successor()\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/graphs_trees/bst_successor/bst_successor_solution.ipynb) for a discussion on algorithms and code solutions."
   ]
  }
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