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Reworked notebook: Added more detail to constraints and test cases. Reworked code and unit test.

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Donne Martin
2015-06-26 05:06:50 -04:00
parent 1278eefa7f
commit fd13918034
1 changed files with 73 additions and 29 deletions
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102
linked-lists/kth-to-last-elem.ipynb
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@@ -13,26 +13,31 @@
"source": [ "source": [
"## Problem: Find the kth to last element of a linked list\n", "## Problem: Find the kth to last element of a linked list\n",
"\n", "\n",
"* [Clarifying Questions](#Clarifying-Questions)\n", "* [Constraints and Assumptions](#Constraints-and-Assumptions)\n",
"* [Test Cases](#Test-Cases)\n", "* [Test Cases](#Test-Cases)\n",
"* [Algorithm](#Algorithm)\n", "* [Algorithm](#Algorithm)\n",
"* [Code](#Code)" "* [Code](#Code)\n",
"* [Unit Test](#Unit-Test)"
] ]
}, },
{ {
"cell_type": "markdown", "cell_type": "markdown",
"metadata": {}, "metadata": {},
"source": [ "source": [
"## Clarifying Questions\n", "## Constraints and Assumptions\n",
"\n", "\n",
"* Is k an integer?\n", "*Problem statements are often intentionally ambiguous. Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
"\n",
"* Can we assume k is a valid integer?\n",
" * Yes\n", " * Yes\n",
"* If k = 0, does this return the last element?\n", "* If k = 0, does this return the last element?\n",
" * Yes\n", " * Yes\n",
"* What happens if k is greater than or equal to the length of the linked list?\n", "* What happens if k is greater than or equal to the length of the linked list?\n",
" * Return None\n", " * Return None\n",
"* Can you use additional data structures?\n", "* Can you use additional data structures?\n",
" * No" " * No\n",
"* Can we assume we already have a linked list class that can be used for this problem?\n",
" * Yes"
] ]
}, },
{ {
@@ -54,7 +59,6 @@
"source": [ "source": [
"## Algorithm\n", "## Algorithm\n",
"\n", "\n",
"* Check for edge cases above, returning None for errors\n",
"* Setup two pointers, current and previous\n", "* Setup two pointers, current and previous\n",
"* Give current a headstart, incrementing it once for k = 1, twice for k = 2, etc\n", "* Give current a headstart, incrementing it once for k = 1, twice for k = 2, etc\n",
"* Increment both pointers until current reaches the end\n", "* Increment both pointers until current reaches the end\n",
@@ -74,7 +78,7 @@
}, },
{ {
"cell_type": "code", "cell_type": "code",
"execution_count": null, "execution_count": 1,
"metadata": { "metadata": {
"collapsed": true "collapsed": true
}, },
@@ -85,7 +89,7 @@
}, },
{ {
"cell_type": "code", "cell_type": "code",
"execution_count": null, "execution_count": 2,
"metadata": { "metadata": {
"collapsed": false "collapsed": false
}, },
@@ -95,49 +99,89 @@
" def kth_to_last_elem(self, k):\n", " def kth_to_last_elem(self, k):\n",
" if self.head is None:\n", " if self.head is None:\n",
" return\n", " return\n",
" if type(k) != int:\n",
" raise ValueError('')\n",
" if k >= len(self):\n", " if k >= len(self):\n",
" return\n", " return\n",
" curr = self.head\n", " curr = self.head\n",
" prev = self.head\n", " prev = self.head\n",
" counter = 0\n", " counter = 0\n",
" \n",
" # Give current a headstart, incrementing it \n",
" # once for k = 1, twice for k = 2, etc\n",
" while counter < k:\n", " while counter < k:\n",
" curr = curr.next\n", " curr = curr.next\n",
" counter += 1\n", " counter += 1\n",
" if curr is None:\n", " if curr is None:\n",
" return\n", " return\n",
" \n",
" # Increment both pointers until current reaches the end\n",
" while curr.next is not None:\n", " while curr.next is not None:\n",
" curr = curr.next\n", " curr = curr.next\n",
" prev = prev.next\n", " prev = prev.next\n",
" return prev.data" " return prev.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", "cell_type": "code",
"execution_count": null, "execution_count": 3,
"metadata": { "metadata": {
"collapsed": false "collapsed": false
}, },
"outputs": [], "outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Test: Empty list\n",
"Test: k >= len(list)\n",
"Test: One element, k = 0\n",
"Test: General case\n",
"Success: test_kth_to_last_elem\n"
]
}
],
"source": [ "source": [
"# Empty list\n", "from nose.tools import assert_equal\n",
"linked_list = MyLinkedList(None)\n", "\n",
"print(linked_list.kth_to_last_elem(0))\n", "class Test(object):\n",
"# k is not an integer\n", " def test_kth_to_last_elem(self):\n",
"print(linked_list.kth_to_last_elem('a'))\n", " print('Test: Empty list')\n",
"# k is >= the length of the linked list\n", " linked_list = MyLinkedList(None)\n",
"print(linked_list.kth_to_last_elem(100))\n", " assert_equal(linked_list.kth_to_last_elem(0), None)\n",
"# One element, k = 0\n", " \n",
"head = Node(2)\n", " print('Test: k >= len(list)')\n",
"linked_list = MyLinkedList(head)\n", " assert_equal(linked_list.kth_to_last_elem(100), None)\n",
"print(linked_list.kth_to_last_elem(0))\n", " \n",
"# General case with many elements, k < length of linked list\n", " print('Test: One element, k = 0')\n",
"linked_list.insert_to_front(1)\n", " head = Node(2)\n",
"linked_list.insert_to_front(3)\n", " linked_list = MyLinkedList(head)\n",
"linked_list.insert_to_front(5)\n", " assert_equal(linked_list.kth_to_last_elem(0), 2)\n",
"linked_list.insert_to_front(7)\n", " \n",
"print(linked_list.kth_to_last_elem(2))" " print('Test: General case')\n",
" linked_list.insert_to_front(1)\n",
" linked_list.insert_to_front(3)\n",
" linked_list.insert_to_front(5)\n",
" linked_list.insert_to_front(7)\n",
" assert_equal(linked_list.kth_to_last_elem(2), 3)\n",
" \n",
" print('Success: test_kth_to_last_elem')\n",
"\n",
"if __name__ == '__main__':\n",
" test = Test()\n",
" test.test_kth_to_last_elem()"
] ]
} }
], ],