Added bst validate challenge.

graphs_trees/bst_validate/bst_validate_challenge.ipynb

@@ -0,0 +1,195 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<small><i>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).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Challenge Notebook"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Determine if a tree is a valid 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",
+    "* Can the tree have duplicates?\n",
+    "    * Yes\n",
+    "* Can we assume we already have a Node class?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "<pre>\n",
+    "Valid:\n",
+    "      5\n",
+    "    /   \\\n",
+    "   5     8\n",
+    "  / \\   /\n",
+    " 4   6 7\n",
+    "\n",
+    "Invalid:\n",
+    "      5\n",
+    "    /   \\\n",
+    "   5     8\n",
+    "  / \\   /\n",
+    " 4   9 7\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_validate/bst_validate_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 validate_bst(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_validate.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "\n",
+    "class TestBstValidate(object):\n",
+    "\n",
+    "    def test_bst_validate(self):\n",
+    "        node = Node(5)\n",
+    "        insert(node, 8)\n",
+    "        insert(node, 5)\n",
+    "        insert(node, 6)\n",
+    "        insert(node, 4)\n",
+    "        insert(node, 7)\n",
+    "        assert_equal(validate_bst(node), True)\n",
+    "\n",
+    "        root = Node(5)\n",
+    "        left = Node(5)\n",
+    "        right = Node(8)\n",
+    "        invalid = Node(20)\n",
+    "        root.left = left\n",
+    "        root.right = right\n",
+    "        root.left.right = invalid\n",
+    "        assert_equal(validate_bst(root), False)\n",
+    "        print('Success: test_bst_validate')\n",
+    "\n",
+    "\n",
+    "def main():\n",
+    "    test = TestBstValidate()\n",
+    "    test.test_bst_validate()\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_validate/bst_validate_solution.ipynb) for a discussion on algorithms and code solutions."
+   ]
+  }
+ ],
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+   "language": "python",
+   "name": "python2"
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