Added find loop start challenge.

linked_lists/find_loop_start/find_loop_start_challenge.ipynb

@@ -0,0 +1,209 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "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/coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Challenge Notebook"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Find the start of a linked list loop.\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",
+    "*Problem statements are sometimes ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
+    "\n",
+    "* Is this a singly linked list?\n",
+    "    * Yes\n",
+    "* Can we assume we are always passed a circular linked list?\n",
+    "    * No\n",
+    "* Can we assume we already have a linked list class that can be used for this problem?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* Empty list -> None\n",
+    "* Not a circular linked list -> None\n",
+    "    * One element\n",
+    "    * Two elements\n",
+    "    * Three or more elements\n",
+    "* General case"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "Refer to the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/coding-challenges/blob/master/linked_lists/find_loop_start/find_loop_start_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 ../linked_list/linked_list.py\n",
+    "%load ../linked_list/linked_list.py"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "class MyLinkedList(LinkedList):\n",
+    "    \n",
+    "    def find_loop_start(self):\n",
+    "        # TODO: Implement me\n",
+    "        pass"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "\n",
+    "\n",
+    "**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_find_loop_start.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "\n",
+    "class TestFindLoopStart(object):\n",
+    "    \n",
+    "    def test_find_loop_start(self):\n",
+    "        print('Test: Empty list')\n",
+    "        linked_list = MyLinkedList()\n",
+    "        assert_equal(linked_list.find_loop_start(), None)\n",
+    "        \n",
+    "        print('Test: Not a circular linked list: One element')\n",
+    "        head = Node(1)\n",
+    "        linked_list = MyLinkedList(head)\n",
+    "        assert_equal(linked_list.find_loop_start(), None)\n",
+    "        \n",
+    "        print('Test: Not a circular linked list: Two elements')\n",
+    "        linked_list.append(2)\n",
+    "        assert_equal(linked_list.find_loop_start(), None)\n",
+    "        \n",
+    "        print('Test: Not a circular linked list: Three or more elements')\n",
+    "        linked_list.append(3)\n",
+    "        assert_equal(linked_list.find_loop_start(), None)\n",
+    "        \n",
+    "        print('Test: General case: Circular linked list')\n",
+    "        node10 = Node(10)\n",
+    "        node9 = Node(9, node10)\n",
+    "        node8 = Node(8, node9)\n",
+    "        node7 = Node(7, node8)\n",
+    "        node6 = Node(6, node7)\n",
+    "        node5 = Node(5, node6)\n",
+    "        node4 = Node(4, node5)\n",
+    "        node3 = Node(3, node4)\n",
+    "        node2 = Node(2, node3)\n",
+    "        node1 = Node(1, node2)\n",
+    "        node0 = Node(0, node1)\n",
+    "        node10.next = node3\n",
+    "        linked_list = MyLinkedList(node0)\n",
+    "        assert_equal(linked_list.find_loop_start(), 3)\n",
+    "        \n",
+    "        print('Success: test_find_loop_start')\n",
+    "\n",
+    "def main():\n",
+    "    test = TestFindLoopStart()\n",
+    "    test.test_find_loop_start()\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/coding-challenges/blob/master/linked_lists/find_loop_start/find_loop_start_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
+}

linked_lists/find_loop_start/find_loop_start_solution.ipynb

@@ -4,7 +4,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://bit.ly/code-notes).</i></small>"
+    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Solution Notebook"
    ]
   },
   {
@@ -26,9 +33,9 @@
    "source": [
     "## Constraints\n",
     "\n",
-    "*Problem statements are often intentionally ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
+    "*Problem statements are sometimes ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
     "\n",
-    "* This is a singly linked list?\n",
+    "* Is this a singly linked list?\n",
     "    * Yes\n",
     "* Can we assume we are always passed a circular linked list?\n",
     "    * No\n",
@@ -42,8 +49,8 @@
    "source": [
     "## Test Cases\n",
     "\n",
-    "* Empty list\n",
+    "* Empty list -> None\n",
-    "* Not a circular linked list\n",
+    "* Not a circular linked list -> None\n",
     "    * One element\n",
     "    * Two elements\n",
     "    * Three or more elements\n",
@@ -84,7 +91,7 @@
    },
    "outputs": [],
    "source": [
-    "%run linked_list.py"
+    "%run ../linked_list/linked_list.py"
    ]
   },
   {
@@ -96,6 +103,7 @@
    "outputs": [],
    "source": [
     "class MyLinkedList(LinkedList):\n",
+    "    \n",
     "    def find_loop_start(self):\n",
     "        if self.head is None or self.head.next is None:\n",
     "            return\n",
@@ -130,13 +138,6 @@
     "## Unit Test"
    ]
   },
-  {
-   "cell_type": "markdown",
-   "metadata": {},
-   "source": [
-    "*It is important to identify and run through general and edge cases from the [Test Cases](#Test-Cases) section by hand.  You generally will not be asked to write a unit test like what is shown below.*"
-   ]
-  },
   {
    "cell_type": "code",
    "execution_count": 3,
@@ -148,19 +149,17 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Test: Empty list\n",
+      "Overwriting test_find_loop_start.py\n"
-      "Test: Not a circular linked list: One element\n",
-      "Test: Not a circular linked list: Two elements\n",
-      "Test: Not a circular linked list: Three or more elements\n",
-      "Test: General case: Circular linked list\n",
-      "Success: test_find_loop_start\n"
      ]
     }
    ],
    "source": [
+    "%%writefile test_find_loop_start.py\n",
     "from nose.tools import assert_equal\n",
     "\n",
-    "class Test(object):\n",
+    "\n",
+    "class TestFindLoopStart(object):\n",
+    "    \n",
     "    def test_find_loop_start(self):\n",
     "        print('Test: Empty list')\n",
     "        linked_list = MyLinkedList()\n",
@@ -197,9 +196,36 @@
     "        \n",
     "        print('Success: test_find_loop_start')\n",
     "\n",
+    "def main():\n",
+    "    test = TestFindLoopStart()\n",
+    "    test.test_find_loop_start()\n",
+    "    \n",
     "if __name__ == '__main__':\n",
-    "    test = Test()\n",
+    "    main()"
-    "    test.test_find_loop_start()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Test: Empty list\n",
+      "Test: Not a circular linked list: One element\n",
+      "Test: Not a circular linked list: Two elements\n",
+      "Test: Not a circular linked list: Three or more elements\n",
+      "Test: General case: Circular linked list\n",
+      "Success: test_find_loop_start\n"
+     ]
+    }
+   ],
+   "source": [
+    "%run -i test_find_loop_start.py"
    ]
   }
  ],

linked_lists/find_loop_start/test_find_loop_start.py

@@ -0,0 +1,47 @@
+from nose.tools import assert_equal
+
+
+class TestFindLoopStart(object):
+    
+    def test_find_loop_start(self):
+        print('Test: Empty list')
+        linked_list = MyLinkedList()
+        assert_equal(linked_list.find_loop_start(), None)
+        
+        print('Test: Not a circular linked list: One element')
+        head = Node(1)
+        linked_list = MyLinkedList(head)
+        assert_equal(linked_list.find_loop_start(), None)
+        
+        print('Test: Not a circular linked list: Two elements')
+        linked_list.append(2)
+        assert_equal(linked_list.find_loop_start(), None)
+        
+        print('Test: Not a circular linked list: Three or more elements')
+        linked_list.append(3)
+        assert_equal(linked_list.find_loop_start(), None)
+        
+        print('Test: General case: Circular linked list')
+        node10 = Node(10)
+        node9 = Node(9, node10)
+        node8 = Node(8, node9)
+        node7 = Node(7, node8)
+        node6 = Node(6, node7)
+        node5 = Node(5, node6)
+        node4 = Node(4, node5)
+        node3 = Node(3, node4)
+        node2 = Node(2, node3)
+        node1 = Node(1, node2)
+        node0 = Node(0, node1)
+        node10.next = node3
+        linked_list = MyLinkedList(node0)
+        assert_equal(linked_list.find_loop_start(), 3)
+        
+        print('Success: test_find_loop_start')
+
+def main():
+    test = TestFindLoopStart()
+    test.test_find_loop_start()
+    
+if __name__ == '__main__':
+    main()