Added tree level lists challenge.

README.md

@@ -207,6 +207,7 @@ Challenges, solutions, and unit tests are presented in the form of **IPython/Jup
 | Implement breadth-first search on a tree | [Challenge](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/tree_bfs/bfs_challenge.ipynb)│[Solution](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/tree_bfs/bfs_solution.ipynb) |
 | Determine the height of a tree | [Challenge](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/tree_height/height_challenge.ipynb)│[Solution](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/tree_height/height_solution.ipynb) |
 | Create a binary search tree with minimal height from a sorted array | [Challenge](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/bst_min/bst_min_challenge.ipynb)│[Solution](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/bst_min/bst_min_solution.ipynb) |
+| Create a linked list for each level of a binary tree | [Challenge](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/tree_level_lists/tree_level_lists_challenge.ipynb)│[Solution](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/tree_level_lists/tree_level_lists_solution.ipynb) |
 | Implement a binary search tree | [Challenge](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/bst/bst_challenge.ipynb)│[Solution](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/bst/bst_solution.ipynb) |
 | Implement depth-first search on a graph |  [Challenge](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/graph_dfs/dfs_challenge.ipynb)│[Solution](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/graph_dfs/dfs_solution.ipynb) |
 | Implement breadth-first search on a graph | [Challenge](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/graph_bfs/bfs_challenge.ipynb)│[Solution](http://nbviewer.ipython.org/github/donnemartin/interactive-coding-challenges/blob/master/graphs_trees/graph_bfs/bfs_solution.ipynb) |

graphs_trees/tree_level_lists/test_tree_level_lists.py

@@ -0,0 +1,42 @@
+from nose.tools import assert_equal
+
+
+class TestTreeLevelLists(object):
+
+    def test_tree_level_lists(self):
+        node = Node(5)
+        insert(node, 3)
+        insert(node, 8)
+        insert(node, 2)
+        insert(node, 4)
+        insert(node, 1)
+        insert(node, 7)
+        insert(node, 6)
+        insert(node, 9)
+        insert(node, 10)
+        insert(node, 11)
+
+        levels = create_level_lists(node)
+        results_list = []
+        for level in levels:
+            results = Results()
+            for node in level:
+                results.add_result(node)
+            results_list.append(results)
+
+        assert_equal(str(results_list[0]), '[5]')
+        assert_equal(str(results_list[1]), '[3, 8]')
+        assert_equal(str(results_list[2]), '[2, 4, 7, 9]')
+        assert_equal(str(results_list[3]), '[1, 6, 10]')
+        assert_equal(str(results_list[4]), '[11]')
+
+        print('Success: test_tree_level_lists')
+
+
+def main():
+    test = TestTreeLevelLists()
+    test.test_tree_level_lists()
+
+
+if __name__ == '__main__':
+    main()

graphs_trees/tree_level_lists/tree_level_lists_challenge.ipynb

@@ -0,0 +1,202 @@
+{
+ "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: Create a linked list for each level of a binary 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",
+    "* Is this a binary search tree?\n",
+    "    * Yes\n",
+    "* Can we assume we already have a Node class with an insert method?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* 5, 3, 8, 2, 4, 1, 7, 6, 9, 10, 11 -> [[5], [3, 8], [2, 4, 7, 9], [1, 6, 10], [11]]"
+   ]
+  },
+  {
+   "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/tree_level_lists/tree_level_lists_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 create_level_lists(root):\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": true
+   },
+   "outputs": [],
+   "source": [
+    "%run ../utils/results.py"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "# %load test_tree_level_lists.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "\n",
+    "class TestTreeLevelLists(object):\n",
+    "\n",
+    "    def test_tree_level_lists(self):\n",
+    "        node = Node(5)\n",
+    "        insert(node, 3)\n",
+    "        insert(node, 8)\n",
+    "        insert(node, 2)\n",
+    "        insert(node, 4)\n",
+    "        insert(node, 1)\n",
+    "        insert(node, 7)\n",
+    "        insert(node, 6)\n",
+    "        insert(node, 9)\n",
+    "        insert(node, 10)\n",
+    "        insert(node, 11)\n",
+    "\n",
+    "        levels = create_level_lists(node)\n",
+    "        results_list = []\n",
+    "        for level in levels:\n",
+    "            results = Results()\n",
+    "            for node in level:\n",
+    "                results.add_result(node)\n",
+    "            results_list.append(results)\n",
+    "\n",
+    "        assert_equal(str(results_list[0]), '[5]')\n",
+    "        assert_equal(str(results_list[1]), '[3, 8]')\n",
+    "        assert_equal(str(results_list[2]), '[2, 4, 7, 9]')\n",
+    "        assert_equal(str(results_list[3]), '[1, 6, 10]')\n",
+    "        assert_equal(str(results_list[4]), '[11]')\n",
+    "\n",
+    "        print('Success: test_tree_level_lists')\n",
+    "\n",
+    "\n",
+    "def main():\n",
+    "    test = TestTreeLevelLists()\n",
+    "    test.test_tree_level_lists()\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/tree_level_lists/tree_level_lists_solution.ipynb) for a discussion on algorithms and code solutions."
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 2",
+   "language": "python",
+   "name": "python2"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 2
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython2",
+   "version": "2.7.10"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}

graphs_trees/tree_level_lists/tree_level_lists_solution.ipynb

@@ -0,0 +1,239 @@
+{
+ "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": [
+    "# Solution Notebook"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Create a linked list for each level of a binary 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",
+    "* Is this a binary search tree?\n",
+    "    * Yes\n",
+    "* Can we assume we already have a Node class with an insert method?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* 5, 3, 8, 2, 4, 1, 7, 6, 9, 10, 11 -> [[5], [3, 8], [2, 4, 7, 9], [1, 6, 10], [11]]"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "We can use either a depth-first or a breadth-first search.  Intuitively, it seems like a breadth-first search might be a better fit as we are creating a linked list for each level.\n",
+    "\n",
+    "We can use a modified breadth-first search that keeps track of parents as we build the linked list for the current level.\n",
+    "\n",
+    "* Append the root to the current level's linked list `current`\n",
+    "* While the `current` is not empty:\n",
+    "    * Add `current` to `results`\n",
+    "    * Set `parents` to `current` to prepare to go one level deeper\n",
+    "    * Clear `current` so it can hold the next level\n",
+    "    * For each `parent` in `parents`, add the children to `current`\n",
+    "* Return the results\n",
+    "    \n",
+    "Complexity:\n",
+    "* Time: O(n)\n",
+    "* Space: O(n)"
+   ]
+  },
+  {
+   "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": [
+    "def create_level_lists(root):\n",
+    "    if root is None:\n",
+    "        return\n",
+    "    results = []\n",
+    "    current = []\n",
+    "    parents = []\n",
+    "    current.append(root)\n",
+    "    while current:\n",
+    "        results.append(current)\n",
+    "        parents = list(current)\n",
+    "        current = []\n",
+    "        for parent in parents:\n",
+    "            if parent.left is not None:\n",
+    "                current.append(parent.left)\n",
+    "            if parent.right is not None:\n",
+    "                current.append(parent.right)\n",
+    "    return results"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "%run ../utils/results.py"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Overwriting test_tree_level_lists.py\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%writefile test_tree_level_lists.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "\n",
+    "class TestTreeLevelLists(object):\n",
+    "\n",
+    "    def test_tree_level_lists(self):\n",
+    "        node = Node(5)\n",
+    "        insert(node, 3)\n",
+    "        insert(node, 8)\n",
+    "        insert(node, 2)\n",
+    "        insert(node, 4)\n",
+    "        insert(node, 1)\n",
+    "        insert(node, 7)\n",
+    "        insert(node, 6)\n",
+    "        insert(node, 9)\n",
+    "        insert(node, 10)\n",
+    "        insert(node, 11)\n",
+    "\n",
+    "        levels = create_level_lists(node)\n",
+    "        results_list = []\n",
+    "        for level in levels:\n",
+    "            results = Results()\n",
+    "            for node in level:\n",
+    "                results.add_result(node)\n",
+    "            results_list.append(results)\n",
+    "\n",
+    "        assert_equal(str(results_list[0]), '[5]')\n",
+    "        assert_equal(str(results_list[1]), '[3, 8]')\n",
+    "        assert_equal(str(results_list[2]), '[2, 4, 7, 9]')\n",
+    "        assert_equal(str(results_list[3]), '[1, 6, 10]')\n",
+    "        assert_equal(str(results_list[4]), '[11]')\n",
+    "\n",
+    "        print('Success: test_tree_level_lists')\n",
+    "\n",
+    "\n",
+    "def main():\n",
+    "    test = TestTreeLevelLists()\n",
+    "    test.test_tree_level_lists()\n",
+    "\n",
+    "\n",
+    "if __name__ == '__main__':\n",
+    "    main()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Success: test_tree_level_lists\n"
+     ]
+    }
+   ],
+   "source": [
+    "%run -i test_tree_level_lists.py"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 2",
+   "language": "python",
+   "name": "python2"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 2
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython2",
+   "version": "2.7.10"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}