diff --git a/linked-lists/add-reverse.ipynb b/linked-lists/add-reverse.ipynb index 444becb..d98c61a 100644 --- a/linked-lists/add-reverse.ipynb +++ b/linked-lists/add-reverse.ipynb @@ -13,22 +13,29 @@ "source": [ "## Problem: Add two numbers whose digits are stored in a linked list in reverse order.\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", "* Do you expect the return to be in reverse order too?\n", " * Yes\n", "* What if one of the inputs is NULL?\n", - " * Return NULL for an invalid operation" + " * Return NULL for an invalid operation\n", + "* How large are these numbers--can they fit in memory?\n", + " * Yes\n", + "* Can we assume we already have a linked list class that can be used for this problem?\n", + " * Yes" ] }, { @@ -55,10 +62,6 @@ "\n", "We could solve this with an iterative or a recursive algorithm, both are well suited for this exercise. We'll use a recursive algorithm for practice with recursion. Note this takes an extra space of O(m) where m is the recursion depth.\n", "\n", - "* Test for error cases\n", - "* Careful with adding if the lists differ\n", - " * Only add if a node is not NULL\n", - " * Alternatively, we could add trailing zeroes to the smaller list\n", "* Base case:\n", " * if first and second lists are NULL AND carry is zero\n", " * Return NULL\n", @@ -73,7 +76,12 @@ "\n", "Complexity:\n", "* Time: O(n)\n", - "* Space: O(n), extra space for result and recursion depth" + "* Space: O(n), extra space for result and recursion depth\n", + "\n", + "Notes:\n", + "* Careful with adding if the lists differ\n", + " * Only add if a node is not NULL\n", + " * Alternatively, we could add trailing zeroes to the smaller list" ] }, { @@ -85,7 +93,7 @@ }, { "cell_type": "code", - "execution_count": null, + "execution_count": 1, "metadata": { "collapsed": true }, @@ -96,7 +104,7 @@ }, { "cell_type": "code", - "execution_count": null, + "execution_count": 2, "metadata": { "collapsed": false }, @@ -114,7 +122,6 @@ " remainder = value % 10\n", " new_carry = 1 if value >= 10 else 0\n", " node = Node(remainder)\n", - " #import pdb; pdb.set_trace()\n", " node.next = self.__add__(first_node.next if first_node is not None else None, \n", " second_node.next if first_node is not None else None, \n", " new_carry)\n", @@ -127,45 +134,80 @@ " return MyLinkedList(head)" ] }, + { + "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(s)\n", + "Test: Add values of different lengths\n", + "Test: Add values of same lengths\n", + "Success: test_add\n" + ] + } + ], "source": [ - "print('Add values of different lengths')\n", - "# Input 1: 6->5->None\n", - "# Input 2: 9->8->7\n", - "# Result: 5->4->8\n", - "first_head = Node(6)\n", - "first_list = MyLinkedList(first_head)\n", - "first_list.append(5)\n", - "second_head = Node(9)\n", - "second_list = MyLinkedList(second_head)\n", - "second_list.append(8)\n", - "second_list.append(7)\n", - "result = MyLinkedList().add(first_list, second_list)\n", - "result.print_list()\n", - "print('Add values of same lengths')\n", - "# Input 1: 6->5->4\n", - "# Input 2: 9->8->7\n", - "# Result: 5->4->2->1\n", - "first_head = Node(6)\n", - "first_list = MyLinkedList(first_head)\n", - "first_list.append(5)\n", - "first_list.append(4)\n", - "second_head = Node(9)\n", - "second_list = MyLinkedList(second_head)\n", - "second_list.append(8)\n", - "second_list.append(7)\n", - "result = MyLinkedList().add(first_list, second_list)\n", - "result.print_list()\n", - "print('Empty list(s)')\n", - "result = MyLinkedList().add(None, None)\n", - "result = MyLinkedList().add(first_head, None)\n", - "result = MyLinkedList().add(None, second_head)" + "from nose.tools import assert_equal\n", + "\n", + "class Test(object):\n", + " def test_add(self):\n", + " print('Test: Empty list(s)')\n", + " assert_equal(MyLinkedList().add(None, None), None)\n", + " assert_equal(MyLinkedList().add(Node(5), None), None)\n", + " assert_equal(MyLinkedList().add(None, Node(10)), None)\n", + "\n", + " print('Test: Add values of different lengths')\n", + " # Input 1: 6->5->None\n", + " # Input 2: 9->8->7\n", + " # Result: 5->4->8\n", + " first_list = MyLinkedList(Node(6))\n", + " first_list.append(5)\n", + " second_list = MyLinkedList(Node(9))\n", + " second_list.append(8)\n", + " second_list.append(7)\n", + " result = MyLinkedList().add(first_list, second_list)\n", + " assert_equal(result.get_all_data(), [5, 4, 8])\n", + "\n", + " print('Test: Add values of same lengths')\n", + " # Input 1: 6->5->4\n", + " # Input 2: 9->8->7\n", + " # Result: 5->4->2->1\n", + " first_head = Node(6)\n", + " first_list = MyLinkedList(first_head)\n", + " first_list.append(5)\n", + " first_list.append(4)\n", + " second_head = Node(9)\n", + " second_list = MyLinkedList(second_head)\n", + " second_list.append(8)\n", + " second_list.append(7)\n", + " result = MyLinkedList().add(first_list, second_list)\n", + " assert_equal(result.get_all_data(), [5, 4, 2, 1])\n", + " \n", + " print('Success: test_add')\n", + "\n", + "if __name__ == '__main__':\n", + " test = Test()\n", + " test.test_add()" ] } ],