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Reworked notebook: Added more detail to constraints and test cases. Reworked algorithm discussion and unit test.
This commit is contained in:
Donne Martin
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25783b5bbb
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@ -13,22 +13,29 @@
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"source": [
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"## Problem: Add two numbers whose digits are stored in a linked list in reverse order.\n",
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"\n",
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"* [Clarifying Questions](#Clarifying-Questions)\n",
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"* [Constraints and Assumptions](#Constraints-and-Assumptions)\n",
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"* [Test Cases](#Test-Cases)\n",
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"* [Algorithm](#Algorithm)\n",
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"* [Code](#Code)"
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"* [Code](#Code)\n",
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"* [Unit Test](#Unit-Test)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Clarifying Questions\n",
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"## Constraints and Assumptions\n",
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"\n",
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"*Problem statements are often intentionally ambiguous. Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
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"\n",
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"* Do you expect the return to be in reverse order too?\n",
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" * Yes\n",
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"* What if one of the inputs is NULL?\n",
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" * Return NULL for an invalid operation"
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" * Return NULL for an invalid operation\n",
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"* How large are these numbers--can they fit in memory?\n",
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" * Yes\n",
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"* Can we assume we already have a linked list class that can be used for this problem?\n",
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" * Yes"
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]
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},
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{
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@ -55,10 +62,6 @@
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"\n",
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"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",
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"\n",
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"* Test for error cases\n",
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"* Careful with adding if the lists differ\n",
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" * Only add if a node is not NULL\n",
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" * Alternatively, we could add trailing zeroes to the smaller list\n",
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"* Base case:\n",
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" * if first and second lists are NULL AND carry is zero\n",
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" * Return NULL\n",
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@ -73,7 +76,12 @@
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"\n",
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"Complexity:\n",
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"* Time: O(n)\n",
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"* Space: O(n), extra space for result and recursion depth"
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"* Space: O(n), extra space for result and recursion depth\n",
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"\n",
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"Notes:\n",
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"* Careful with adding if the lists differ\n",
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" * Only add if a node is not NULL\n",
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" * Alternatively, we could add trailing zeroes to the smaller list"
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]
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},
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{
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@ -85,7 +93,7 @@
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"execution_count": 1,
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"metadata": {
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"collapsed": true
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},
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@ -96,7 +104,7 @@
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"execution_count": 2,
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"metadata": {
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"collapsed": false
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},
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@ -114,7 +122,6 @@
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" remainder = value % 10\n",
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" new_carry = 1 if value >= 10 else 0\n",
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" node = Node(remainder)\n",
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" #import pdb; pdb.set_trace()\n",
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" node.next = self.__add__(first_node.next if first_node is not None else None, \n",
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" second_node.next if first_node is not None else None, \n",
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" new_carry)\n",
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@ -127,28 +134,61 @@
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" return MyLinkedList(head)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Unit Test"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"*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.*"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"execution_count": 3,
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"metadata": {
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"collapsed": false
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},
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"outputs": [],
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Test: Empty list(s)\n",
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"Test: Add values of different lengths\n",
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"Test: Add values of same lengths\n",
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"Success: test_add\n"
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]
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}
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],
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"source": [
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"print('Add values of different lengths')\n",
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"from nose.tools import assert_equal\n",
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"\n",
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"class Test(object):\n",
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" def test_add(self):\n",
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" print('Test: Empty list(s)')\n",
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" assert_equal(MyLinkedList().add(None, None), None)\n",
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" assert_equal(MyLinkedList().add(Node(5), None), None)\n",
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" assert_equal(MyLinkedList().add(None, Node(10)), None)\n",
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"\n",
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" print('Test: Add values of different lengths')\n",
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" # Input 1: 6->5->None\n",
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" # Input 2: 9->8->7\n",
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" # Result: 5->4->8\n",
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"first_head = Node(6)\n",
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"first_list = MyLinkedList(first_head)\n",
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" first_list = MyLinkedList(Node(6))\n",
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" first_list.append(5)\n",
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"second_head = Node(9)\n",
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"second_list = MyLinkedList(second_head)\n",
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" second_list = MyLinkedList(Node(9))\n",
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" second_list.append(8)\n",
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" second_list.append(7)\n",
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" result = MyLinkedList().add(first_list, second_list)\n",
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"result.print_list()\n",
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"print('Add values of same lengths')\n",
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" assert_equal(result.get_all_data(), [5, 4, 8])\n",
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"\n",
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" print('Test: Add values of same lengths')\n",
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" # Input 1: 6->5->4\n",
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" # Input 2: 9->8->7\n",
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" # Result: 5->4->2->1\n",
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@ -161,11 +201,13 @@
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" second_list.append(8)\n",
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" second_list.append(7)\n",
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" result = MyLinkedList().add(first_list, second_list)\n",
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"result.print_list()\n",
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"print('Empty list(s)')\n",
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"result = MyLinkedList().add(None, None)\n",
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"result = MyLinkedList().add(first_head, None)\n",
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"result = MyLinkedList().add(None, second_head)"
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" assert_equal(result.get_all_data(), [5, 4, 2, 1])\n",
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" \n",
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" print('Success: test_add')\n",
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"\n",
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"if __name__ == '__main__':\n",
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" test = Test()\n",
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" test.test_add()"
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]
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}
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],
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