From 1278eefa7ff6123d290d8ed360cc290a9ec83d8e Mon Sep 17 00:00:00 2001 From: Donne Martin Date: Fri, 26 Jun 2015 05:06:11 -0400 Subject: [PATCH] Reworked notebook: Added more detail to constraints and test cases. Reworked algorithm discussion and unit test. --- linked-lists/find-loop-start.ipynb | 143 +++++++++++++++++++---------- 1 file changed, 93 insertions(+), 50 deletions(-) diff --git a/linked-lists/find-loop-start.ipynb b/linked-lists/find-loop-start.ipynb index 8bf8363..8f6fc49 100644 --- a/linked-lists/find-loop-start.ipynb +++ b/linked-lists/find-loop-start.ipynb @@ -13,22 +13,27 @@ "source": [ "## Problem: Find the start of a linked list loop.\n", "\n", - "* [Clarifying Questions](#Clarifying-Questions)\n", + "* [Constraints and Assumptions](#Constraints-and-Assumptions)\n", "* [Test Cases](#Test-Cases)\n", "* [Algorithm](#Algorithm)\n", - "* [Code](#Code)" + "* [Code](#Code)\n", + "* [Unit Test](#Unit-Test)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ - "## Clarifying Questions\n", + "## Constraints and Assumptions\n", + "\n", + "*Problem statements are often intentionally ambiguous. Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n", "\n", "* This is a singly linked list?\n", " * Yes\n", "* Can we assume we are always passed a circular linked list?\n", - " * No" + " * No\n", + "* Can we assume we already have a linked list class that can be used for this problem?\n", + " * Yes" ] }, { @@ -51,10 +56,10 @@ "source": [ "## Algorithm\n", "\n", - "* Check for an empty list\n", "* Use two pointers i, j, initialized to the head\n", - "* j is incremented twice as fast as i\n", - " * If j's next is NULL, we do not have a circular list\n", + "* Increment i and j until they meet\n", + " * j is incremented twice as fast as i\n", + " * If j's next is NULL, we do not have a circular list\n", "* When i and j meet, move j to the head\n", "* Increment i and j one node at a time until they meet\n", "* Where they meet is the start of the loop\n", @@ -73,7 +78,7 @@ }, { "cell_type": "code", - "execution_count": null, + "execution_count": 1, "metadata": { "collapsed": true }, @@ -84,7 +89,7 @@ }, { "cell_type": "code", - "execution_count": null, + "execution_count": 2, "metadata": { "collapsed": false }, @@ -98,65 +103,103 @@ " j = self.head\n", " i = i.next\n", " j = j.next.next\n", + " \n", + " # Increment i and j until they meet\n", + " # j is incremented twice as fast as i\n", " while j != i:\n", " i = i.next\n", " if j is None or j.next is None:\n", " return\n", " j = j.next.next\n", + " \n", + " # When i and j meet, move j to the head\n", " j = self.head\n", + " \n", + " # Increment i and j one node at a time until \n", + " # they meet, which is the start of the loop\n", " while j != i:\n", " i = i.next\n", " j = j.next\n", " return i.data" ] }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## 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": null, + "execution_count": 3, "metadata": { "collapsed": false }, - "outputs": [], + "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": [ - "print('Empty list')\n", - "linked_list = MyLinkedList()\n", - "print(linked_list.find_loop_start())\n", - "print('Not a circular linked list')\n", - "print('One element')\n", - "head = Node(1)\n", - "linked_list = MyLinkedList(head)\n", - "print(linked_list.find_loop_start())\n", - "print('Two elements')\n", - "linked_list.append(2)\n", - "print(linked_list.find_loop_start())\n", - "print('Three or more elements')\n", - "linked_list.append(3)\n", - "print(linked_list.find_loop_start())\n", - "print('General case')\n", - "node0 = Node(0)\n", - "node1 = Node(1)\n", - "node2 = Node(2)\n", - "node3 = Node(3)\n", - "node4 = Node(4)\n", - "node5 = Node(5)\n", - "node6 = Node(6)\n", - "node7 = Node(7)\n", - "node8 = Node(8)\n", - "node9 = Node(9)\n", - "node10 = Node(10)\n", - "node0.next = node1\n", - "node1.next = node2\n", - "node2.next = node3\n", - "node3.next = node4\n", - "node4.next = node5\n", - "node5.next = node6\n", - "node6.next = node7\n", - "node7.next = node8\n", - "node8.next = node9\n", - "node9.next = node10\n", - "node10.next = node3\n", - "linked_list = MyLinkedList(node0)\n", - "print(linked_list.find_loop_start())" + "from nose.tools import assert_equal\n", + "\n", + "class Test(object):\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", + "if __name__ == '__main__':\n", + " test = Test()\n", + " test.test_find_loop_start()" ] } ],