{ "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges)." ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "# Solution Notebook" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Problem: Partition a linked list around a value x, such that all nodes less than x come before all nodes greater than or equal to x.\n", "\n", "* [Constraints](#Constraints)\n", "* [Test Cases](#Test-Cases)\n", "* [Algorithm](#Algorithm)\n", "* [Code](#Code)\n", "* [Unit Test](#Unit-Test)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Constraints\n", "\n", "* Do we expect the function to return a new list?\n", " * Yes\n", "* Can we assume the input x is valid?\n", " * Yes\n", "* Can we assume we already have a linked list class that can be used for this problem?\n", " * Yes\n", "* Can we create additional data structures?\n", " * Yes\n", "* Can we assume this fits in memory?\n", " * Yes" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Test Cases\n", "\n", "* Empty list -> []\n", "* One element list -> [element]\n", "* Left linked list is empty\n", "* Right linked list is empty\n", "* General case\n", " * Partition = 10\n", " * Input: 4, 3, 13, 8, 10, 1, 10, 12\n", " * Output: 4, 3, 8, 1, 10, 10, 13, 12" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Algorithm\n", "\n", "* Create left and right linked lists\n", "* For each element in the list\n", " * If elem < x, append to the left list\n", " * else, append to the right list\n", "* Merge left and right lists\n", "\n", "Complexity:\n", "* Time: O(n)\n", "* Space: O(n)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Code" ] }, { "cell_type": "code", "execution_count": 1, "metadata": { "collapsed": true }, "outputs": [], "source": [ "%run ../linked_list/linked_list.py" ] }, { "cell_type": "code", "execution_count": 2, "metadata": { "collapsed": false }, "outputs": [], "source": [ "class MyLinkedList(LinkedList):\n", "\n", " def partition(self, data):\n", " if self.head is None:\n", " return\n", " left = MyLinkedList(None)\n", " right = MyLinkedList(None)\n", " curr = self.head\n", "\n", " # Build the left and right lists\n", " while curr is not None:\n", " if curr.data < data:\n", " left.append(curr.data)\n", " elif curr.data == data:\n", " right.insert_to_front(curr.data)\n", " else:\n", " right.append(curr.data)\n", " curr = curr.next\n", " curr_left = left.head\n", " if curr_left is None:\n", " return right\n", " else:\n", " # Merge the two lists\n", " while curr_left.next is not None:\n", " curr_left = curr_left.next\n", " curr_left.next = right.head\n", " return left" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Unit Test" ] }, { "cell_type": "code", "execution_count": 3, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Overwriting test_partition.py\n" ] } ], "source": [ "%%writefile test_partition.py\n", "from nose.tools import assert_equal\n", "\n", "\n", "class TestPartition(object):\n", "\n", " def test_partition(self):\n", " print('Test: Empty list')\n", " linked_list = MyLinkedList(None)\n", " linked_list.partition(10)\n", " assert_equal(linked_list.get_all_data(), [])\n", "\n", " print('Test: One element list, left list empty')\n", " linked_list = MyLinkedList(Node(5))\n", " linked_list.partition(0)\n", " assert_equal(linked_list.get_all_data(), [5])\n", "\n", " print('Test: Right list is empty')\n", " linked_list = MyLinkedList(Node(5))\n", " linked_list.partition(10)\n", " assert_equal(linked_list.get_all_data(), [5])\n", "\n", " print('Test: General case')\n", " # Partition = 10\n", " # Input: 4, 3, 13, 8, 10, 1, 14, 10, 12\n", " # Output: 4, 3, 8, 1, 10, 10, 13, 14, 12\n", " linked_list = MyLinkedList(Node(12))\n", " linked_list.insert_to_front(10)\n", " linked_list.insert_to_front(14)\n", " linked_list.insert_to_front(1)\n", " linked_list.insert_to_front(10)\n", " linked_list.insert_to_front(8)\n", " linked_list.insert_to_front(13)\n", " linked_list.insert_to_front(3)\n", " linked_list.insert_to_front(4)\n", " partitioned_list = linked_list.partition(10)\n", " assert_equal(partitioned_list.get_all_data(),\n", " [4, 3, 8, 1, 10, 10, 13, 14, 12])\n", "\n", " print('Success: test_partition')\n", "\n", "\n", "def main():\n", " test = TestPartition()\n", " test.test_partition()\n", "\n", "\n", "if __name__ == '__main__':\n", " main()" ] }, { "cell_type": "code", "execution_count": 4, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Test: Empty list\n", "Test: One element list, left list empty\n", "Test: Right list is empty\n", "Test: General case\n", "Success: test_partition\n" ] } ], "source": [ "run -i test_partition.py" ] } ], "metadata": { "kernelspec": { "display_name": "Python 3", "language": "python", "name": "python3" }, "language_info": { "codemirror_mode": { "name": "ipython", "version": 3 }, "file_extension": ".py", "mimetype": "text/x-python", "name": "python", "nbconvert_exporter": "python", "pygments_lexer": "ipython3", "version": "3.5.0" } }, "nbformat": 4, "nbformat_minor": 0 }