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Reworked notebook: Added more detail to constraints and test cases. Reworked code and unit test.
This commit is contained in:
Donne Martin
parent
1278eefa7f
commit
fd13918034
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@ -13,26 +13,31 @@
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"source": [
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"## Problem: Find the kth to last element of a linked list\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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"* Is k an integer?\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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"* Can we assume k is a valid integer?\n",
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" * Yes\n",
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"* If k = 0, does this return the last element?\n",
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" * Yes\n",
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"* What happens if k is greater than or equal to the length of the linked list?\n",
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" * Return None\n",
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"* Can you use additional data structures?\n",
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" * No"
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" * No\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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@ -54,7 +59,6 @@
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"source": [
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"## Algorithm\n",
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"\n",
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"* Check for edge cases above, returning None for errors\n",
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"* Setup two pointers, current and previous\n",
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"* Give current a headstart, incrementing it once for k = 1, twice for k = 2, etc\n",
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"* Increment both pointers until current reaches the end\n",
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@ -74,7 +78,7 @@
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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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@ -85,7 +89,7 @@
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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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@ -95,49 +99,89 @@
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" def kth_to_last_elem(self, k):\n",
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" if self.head is None:\n",
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" return\n",
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" if type(k) != int:\n",
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" raise ValueError('')\n",
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" if k >= len(self):\n",
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" return\n",
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" curr = self.head\n",
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" prev = self.head\n",
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" counter = 0\n",
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" \n",
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" # Give current a headstart, incrementing it \n",
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" # once for k = 1, twice for k = 2, etc\n",
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" while counter < k:\n",
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" curr = curr.next\n",
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" counter += 1\n",
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" if curr is None:\n",
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" return\n",
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" \n",
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" # Increment both pointers until current reaches the end\n",
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" while curr.next is not None:\n",
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" curr = curr.next\n",
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" prev = prev.next\n",
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" return prev.data"
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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\n",
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"Test: k >= len(list)\n",
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"Test: One element, k = 0\n",
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"Test: General case\n",
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"Success: test_kth_to_last_elem\n"
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]
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}
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],
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"source": [
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"# Empty list\n",
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"linked_list = MyLinkedList(None)\n",
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"print(linked_list.kth_to_last_elem(0))\n",
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"# k is not an integer\n",
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"print(linked_list.kth_to_last_elem('a'))\n",
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"# k is >= the length of the linked list\n",
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"print(linked_list.kth_to_last_elem(100))\n",
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"# One element, k = 0\n",
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"head = Node(2)\n",
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"linked_list = MyLinkedList(head)\n",
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"print(linked_list.kth_to_last_elem(0))\n",
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"# General case with many elements, k < length of linked list\n",
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"linked_list.insert_to_front(1)\n",
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"linked_list.insert_to_front(3)\n",
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"linked_list.insert_to_front(5)\n",
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"linked_list.insert_to_front(7)\n",
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"print(linked_list.kth_to_last_elem(2))"
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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_kth_to_last_elem(self):\n",
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" print('Test: Empty list')\n",
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" linked_list = MyLinkedList(None)\n",
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" assert_equal(linked_list.kth_to_last_elem(0), None)\n",
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" \n",
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" print('Test: k >= len(list)')\n",
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" assert_equal(linked_list.kth_to_last_elem(100), None)\n",
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" \n",
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" print('Test: One element, k = 0')\n",
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" head = Node(2)\n",
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" linked_list = MyLinkedList(head)\n",
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" assert_equal(linked_list.kth_to_last_elem(0), 2)\n",
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" \n",
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" print('Test: General case')\n",
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" linked_list.insert_to_front(1)\n",
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" linked_list.insert_to_front(3)\n",
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" linked_list.insert_to_front(5)\n",
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" linked_list.insert_to_front(7)\n",
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" assert_equal(linked_list.kth_to_last_elem(2), 3)\n",
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" \n",
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" print('Success: test_kth_to_last_elem')\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_kth_to_last_elem()"
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]
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}
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],
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