diff --git a/linked-lists/remove-duplicates.ipynb b/linked-lists/remove-duplicates.ipynb new file mode 100644 index 0000000..96e5863 --- /dev/null +++ b/linked-lists/remove-duplicates.ipynb @@ -0,0 +1,257 @@ +{ + "cells": [ + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## Problem: Remove duplicates from a linked list\n", + "\n", + "* [Clarifying Questions](#Clarifying-Questions)\n", + "* [Test Cases](#Test-Cases)\n", + "* [Algorithm: Hash Map Lookup](#Algorithm:-Hash-Map-Lookup)\n", + "* [Code: Hash Map Lookup](#Code:-Hash-Map-Lookup)\n", + "* [Algorithm: In-Place](#Algorithm:-In-Place)\n", + "* [Code: In-Place](#Code:-In-Place)" + ] + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## Clarifying Questions\n", + "\n", + "* Do we assume the linked list class already exists?\n", + " * No, create one\n", + "* Is this a singly or doubly linked list?\n", + " * Singly\n", + "* Can you insert NULL values in the list?\n", + " * No\n", + "* Can use additional data structures?\n", + " * Implement both solutions" + ] + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## Test Cases\n", + "\n", + "* Empty linked list\n", + "* One element linked list\n", + "* Multiple elements\n", + "* No duplicates\n", + "* One or more duplicates" + ] + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## Algorithm: Hash Map Lookup\n", + "\n", + "* For each node\n", + " * If the node's value is in the hash map\n", + " * Delete the node\n", + " * Else\n", + " * Add node's value to the hash map\n", + "\n", + "Complexity:\n", + "* Time: O(n)\n", + "* Space: O(m) where m is the number of values in the hash map\n", + "\n", + "Note:\n", + "* Deletion requires two pointers, one to the previous node and one to the current node" + ] + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## Code: Hash Map Lookup" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "class Node(object):\n", + " def __init__(self, data):\n", + " self.next = None\n", + " self.data = data\n", + "\n", + "class LinkedList(object):\n", + " def __init__(self, head):\n", + " self.head = head\n", + " \n", + " def remove_dupes(self):\n", + " seen_data = set()\n", + " curr = self.head\n", + " prev = None\n", + " while curr is not None:\n", + " if curr.data in seen_data:\n", + " prev.next = curr.next\n", + " else:\n", + " seen_data.add(curr.data)\n", + " prev = curr\n", + " curr = curr.next\n", + " \n", + " def insert_to_front(self, data):\n", + " if data is None:\n", + " return\n", + " node = Node(data)\n", + " if self.head is None:\n", + " self.head = node\n", + " else:\n", + " node.next = self.head\n", + " self.head = node \n", + " \n", + " def print_list(self):\n", + " curr = self.head\n", + " while curr is not None:\n", + " print(curr.data)\n", + " curr = curr.next\n", + " \n", + "# Empty linked list\n", + "linked_list = LinkedList(None)\n", + "linked_list.remove_dupes()\n", + "linked_list.print_list()\n", + "# One element linked list\n", + "head = Node(2)\n", + "linked_list = LinkedList(head)\n", + "linked_list.remove_dupes()\n", + "linked_list.print_list()\n", + "# Multiple elements\n", + "# One or more duplicates\n", + "linked_list.insert_to_front(1)\n", + "linked_list.insert_to_front(3)\n", + "linked_list.insert_to_front(1)\n", + "linked_list.insert_to_front(1)\n", + "linked_list.remove_dupes()\n", + "linked_list.print_list()\n", + "# No duplicates\n", + "linked_list.remove_dupes()\n", + "linked_list.print_list()" + ] + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## Algorithm: In-Place\n", + "\n", + "* For each node\n", + " * Compare node with every other node\n", + " * If the node's value is in the hash map\n", + " * Delete the node\n", + " * Else\n", + " * Add node's value to the hash map\n", + "\n", + "Complexity:\n", + "* Time: O(n^2)\n", + "* Space: In-place\n", + "\n", + "Note:\n", + "* Deletion requires two pointers, one to the previous node and one to the current node\n", + "* We'll need to use a 'runner' to check every other node and compare it to the current node" + ] + }, + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "## Code: In-Place" + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": { + "collapsed": false + }, + "outputs": [], + "source": [ + "class Node(object):\n", + " def __init__(self, data):\n", + " self.next = None\n", + " self.data = data\n", + "\n", + "class LinkedList(object):\n", + " def __init__(self, head):\n", + " self.head = head\n", + " \n", + " def remove_dupes(self):\n", + " curr = self.head\n", + " while curr is not None:\n", + " runner = curr\n", + " while runner.next is not None:\n", + " if runner.next.data == curr.data:\n", + " runner.next = runner.next.next\n", + " else:\n", + " runner = runner.next\n", + " curr = curr.next\n", + " \n", + " def insert_to_front(self, data):\n", + " if data is None:\n", + " return\n", + " node = Node(data)\n", + " if self.head is None:\n", + " self.head = node\n", + " else:\n", + " node.next = self.head\n", + " self.head = node \n", + " \n", + " def print_list(self):\n", + " curr = self.head\n", + " while curr is not None:\n", + " print(curr.data)\n", + " curr = curr.next\n", + " \n", + "# Empty linked list\n", + "linked_list = LinkedList(None)\n", + "linked_list.remove_dupes()\n", + "linked_list.print_list()\n", + "# One element linked list\n", + "head = Node(2)\n", + "linked_list = LinkedList(head)\n", + "linked_list.remove_dupes()\n", + "linked_list.print_list()\n", + "# Multiple elements\n", + "# One or more duplicates\n", + "linked_list.insert_to_front(1)\n", + "linked_list.insert_to_front(3)\n", + "linked_list.insert_to_front(1)\n", + "linked_list.insert_to_front(1)\n", + "linked_list.remove_dupes()\n", + "linked_list.print_list()\n", + "# No duplicates\n", + "linked_list.remove_dupes()\n", + "linked_list.print_list()" + ] + } + ], + "metadata": { + "kernelspec": { + "display_name": "Python 2", + "language": "python", + "name": "python2" + }, + "language_info": { + "codemirror_mode": { + "name": "ipython", + "version": 2 + }, + "file_extension": ".py", + "mimetype": "text/x-python", + "name": "python", + "nbconvert_exporter": "python", + "pygments_lexer": "ipython2", + "version": "2.7.9" + } + }, + "nbformat": 4, + "nbformat_minor": 0 +}