diff --git a/graphs_trees/bst_second_largest/__init__.py b/graphs_trees/bst_second_largest/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/graphs_trees/bst_second_largest/bst_second_largest_challenge.ipynb b/graphs_trees/bst_second_largest/bst_second_largest_challenge.ipynb
new file mode 100644
index 0000000..0ebb78c
--- /dev/null
+++ b/graphs_trees/bst_second_largest/bst_second_largest_challenge.ipynb
@@ -0,0 +1,212 @@
+{
+ "cells": [
+ {
+ "cell_type": "markdown",
+ "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 second largest 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 this is called on a None input or a single node, should we raise an exception?\n",
+ " * Yes\n",
+ " * None -> TypeError\n",
+ " * Single node -> ValueError\n",
+ "* Can we assume we already have a Node class with an insert method?\n",
+ " * Yes\n",
+ "* Can we assume this fits memory?\n",
+ " * Yes"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "## Test Cases\n",
+ "\n",
+ "* None or single node -> Exception\n",
+ "\n",
+ "\n",
+ "Input:\n",
+ " _10_\n",
+ " _/ \\_ \n",
+ " 5 15\n",
+ " / \\ / \\\n",
+ " 3 8 12 20\n",
+ " / \\ \\\n",
+ " 2 4 30\n",
+ "\n",
+ "Output: 20\n",
+ "\n",
+ "Input:\n",
+ " 10\n",
+ " / \n",
+ " 5\n",
+ " / \\\n",
+ " 3 7\n",
+ "Output: 7\n",
+ "
"
+ ]
+ },
+ {
+ "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/check_balance/check_balance_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": [
+ "class Solution(Bst):\n",
+ "\n",
+ " def find_second_largest(self):\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_second_largest.py\n",
+ "from nose.tools import assert_equal, assert_raises\n",
+ "\n",
+ "\n",
+ "class TestBstSecondLargest(object):\n",
+ "\n",
+ " def test_bst_second_largest(self):\n",
+ " bst = Solution(None)\n",
+ " assert_raises(TypeError, bst.find_second_largest)\n",
+ " root = Node(10)\n",
+ " bst = Solution(root)\n",
+ " node5 = bst.insert(5)\n",
+ " node15 = bst.insert(15)\n",
+ " node3 = bst.insert(3)\n",
+ " node8 = bst.insert(8)\n",
+ " node12 = bst.insert(12)\n",
+ " node20 = bst.insert(20)\n",
+ " node2 = bst.insert(2)\n",
+ " node4 = bst.insert(4)\n",
+ " node30 = bst.insert(30)\n",
+ " assert_equal(bst.find_second_largest(), node20)\n",
+ " root = Node(10)\n",
+ " bst = Solution(root)\n",
+ " node5 = bst.insert(5)\n",
+ " node3 = bst.insert(3)\n",
+ " node7 = bst.insert(7)\n",
+ " assert_equal(bst.find_second_largest(), node7)\n",
+ " print('Success: test_bst_second_largest')\n",
+ "\n",
+ "\n",
+ "def main():\n",
+ " test = TestBstSecondLargest()\n",
+ " test.test_bst_second_largest()\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/check_balance/check_balance_solution.ipynb) for a discussion on algorithms and code solutions."
+ ]
+ }
+ ],
+ "metadata": {
+ "kernelspec": {
+ "display_name": "Python 3",
+ "language": "python",
+ "name": "python3"
+ },
+ "language_info": {
+ "codemirror_mode": {
+ "name": "ipython",
+ "version": 3
+ },
+ "file_extension": ".py",
+ "mimetype": "text/x-python",
+ "name": "python",
+ "nbconvert_exporter": "python",
+ "pygments_lexer": "ipython3",
+ "version": "3.5.0"
+ }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}
diff --git a/graphs_trees/bst_second_largest/bst_second_largest_solution.ipynb b/graphs_trees/bst_second_largest/bst_second_largest_solution.ipynb
new file mode 100644
index 0000000..6da1202
--- /dev/null
+++ b/graphs_trees/bst_second_largest/bst_second_largest_solution.ipynb
@@ -0,0 +1,271 @@
+{
+ "cells": [
+ {
+ "cell_type": "markdown",
+ "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: Find the second largest 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)"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "## Constraints\n",
+ "\n",
+ "* If this is called on a None input or a single node, should we raise an exception?\n",
+ " * Yes\n",
+ " * None -> TypeError\n",
+ " * Single node -> ValueError\n",
+ "* Can we assume we already have a Node class with an insert method?\n",
+ " * Yes\n",
+ "* Can we assume this fits memory?\n",
+ " * Yes"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "## Test Cases\n",
+ "\n",
+ "* None or single node -> Exception\n",
+ "\n",
+ "\n",
+ "Input:\n",
+ " _10_\n",
+ " _/ \\_ \n",
+ " 5 15\n",
+ " / \\ / \\\n",
+ " 3 8 12 20\n",
+ " / \\ \\\n",
+ " 2 4 30\n",
+ "\n",
+ "Output: 20\n",
+ "\n",
+ "Input:\n",
+ " 10\n",
+ " / \n",
+ " 5\n",
+ " / \\\n",
+ " 3 7\n",
+ "Output: 7\n",
+ "
"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "## Algorithm\n",
+ "\n",
+ "\n",
+ "\n",
+ "If there is no right node, the second largest is the right most left subtree:\n",
+ "\n",
+ " 10\n",
+ " / \n",
+ " 5\n",
+ " / \\\n",
+ " 3 7\n",
+ "\n",
+ "If there is a right node and the right node has children, recurse to that right child:\n",
+ "\n",
+ " _10_\n",
+ " _/ \\_ \n",
+ " 5 15\n",
+ " / \\ / \\\n",
+ " 3 8 12 20\n",
+ " / \\ \\\n",
+ " 2 4 30\n",
+ "\n",
+ "Eventually we'll get to the following scenario:\n",
+ "\n",
+ " 20\n",
+ " \\\n",
+ " 30\n",
+ "\n",
+ "If the right node has no children, the second largest is the current node.\n",
+ "\n",
+ "
\n",
+ "\n",
+ "Complexity:\n",
+ "* Time: O(h)\n",
+ "* Space: O(h), where h is the height of the tree"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "## Code"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 1,
+ "metadata": {
+ "collapsed": true
+ },
+ "outputs": [],
+ "source": [
+ "%run ../bst/bst.py"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 2,
+ "metadata": {
+ "collapsed": false
+ },
+ "outputs": [],
+ "source": [
+ "class Solution(Bst):\n",
+ "\n",
+ " def _find_second_largest(self, node):\n",
+ " if node.right is not None:\n",
+ " if node.right.left is not None or node.right.right is not None:\n",
+ " return self._find_second_largest(node.right)\n",
+ " else:\n",
+ " return node\n",
+ " else:\n",
+ " return self._find_right_most_node(node.left)\n",
+ "\n",
+ " def _find_right_most_node(self, node):\n",
+ " if node.right is not None:\n",
+ " return self._find_right_most_node(node.right)\n",
+ " else:\n",
+ " return node\n",
+ "\n",
+ " def find_second_largest(self):\n",
+ " if self.root is None:\n",
+ " raise TypeError('root cannot be None')\n",
+ " if self.root.right is None and self.root.left is None:\n",
+ " raise ValueError('root must have at least one child')\n",
+ " return self._find_second_largest(self.root)"
+ ]
+ },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "## Unit Test"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 3,
+ "metadata": {
+ "collapsed": false
+ },
+ "outputs": [
+ {
+ "name": "stdout",
+ "output_type": "stream",
+ "text": [
+ "Overwriting test_bst_second_largest.py\n"
+ ]
+ }
+ ],
+ "source": [
+ "%%writefile test_bst_second_largest.py\n",
+ "from nose.tools import assert_equal, assert_raises\n",
+ "\n",
+ "\n",
+ "class TestBstSecondLargest(object):\n",
+ "\n",
+ " def test_bst_second_largest(self):\n",
+ " bst = Solution(None)\n",
+ " assert_raises(TypeError, bst.find_second_largest)\n",
+ " root = Node(10)\n",
+ " bst = Solution(root)\n",
+ " node5 = bst.insert(5)\n",
+ " node15 = bst.insert(15)\n",
+ " node3 = bst.insert(3)\n",
+ " node8 = bst.insert(8)\n",
+ " node12 = bst.insert(12)\n",
+ " node20 = bst.insert(20)\n",
+ " node2 = bst.insert(2)\n",
+ " node4 = bst.insert(4)\n",
+ " node30 = bst.insert(30)\n",
+ " assert_equal(bst.find_second_largest(), node20)\n",
+ " root = Node(10)\n",
+ " bst = Solution(root)\n",
+ " node5 = bst.insert(5)\n",
+ " node3 = bst.insert(3)\n",
+ " node7 = bst.insert(7)\n",
+ " assert_equal(bst.find_second_largest(), node7)\n",
+ " print('Success: test_bst_second_largest')\n",
+ "\n",
+ "\n",
+ "def main():\n",
+ " test = TestBstSecondLargest()\n",
+ " test.test_bst_second_largest()\n",
+ "\n",
+ "\n",
+ "if __name__ == '__main__':\n",
+ " main()"
+ ]
+ },
+ {
+ "cell_type": "code",
+ "execution_count": 4,
+ "metadata": {
+ "collapsed": false
+ },
+ "outputs": [
+ {
+ "name": "stdout",
+ "output_type": "stream",
+ "text": [
+ "Success: test_bst_second_largest\n"
+ ]
+ }
+ ],
+ "source": [
+ "%run -i test_bst_second_largest.py"
+ ]
+ }
+ ],
+ "metadata": {
+ "kernelspec": {
+ "display_name": "Python 3",
+ "language": "python",
+ "name": "python3"
+ },
+ "language_info": {
+ "codemirror_mode": {
+ "name": "ipython",
+ "version": 3
+ },
+ "file_extension": ".py",
+ "mimetype": "text/x-python",
+ "name": "python",
+ "nbconvert_exporter": "python",
+ "pygments_lexer": "ipython3",
+ "version": "3.5.0"
+ }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}
diff --git a/graphs_trees/bst_second_largest/test_bst_second_largest.py b/graphs_trees/bst_second_largest/test_bst_second_largest.py
new file mode 100644
index 0000000..a5a67db
--- /dev/null
+++ b/graphs_trees/bst_second_largest/test_bst_second_largest.py
@@ -0,0 +1,36 @@
+from nose.tools import assert_equal, assert_raises
+
+
+class TestBstSecondLargest(object):
+
+ def test_bst_second_largest(self):
+ bst = Solution(None)
+ assert_raises(TypeError, bst.find_second_largest)
+ root = Node(10)
+ bst = Solution(root)
+ node5 = bst.insert(5)
+ node15 = bst.insert(15)
+ node3 = bst.insert(3)
+ node8 = bst.insert(8)
+ node12 = bst.insert(12)
+ node20 = bst.insert(20)
+ node2 = bst.insert(2)
+ node4 = bst.insert(4)
+ node30 = bst.insert(30)
+ assert_equal(bst.find_second_largest(), node20)
+ root = Node(10)
+ bst = Solution(root)
+ node5 = bst.insert(5)
+ node3 = bst.insert(3)
+ node7 = bst.insert(7)
+ assert_equal(bst.find_second_largest(), node7)
+ print('Success: test_bst_second_largest')
+
+
+def main():
+ test = TestBstSecondLargest()
+ test.test_bst_second_largest()
+
+
+if __name__ == '__main__':
+ main()
\ No newline at end of file