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Added notebook solving the following: Remove duplicates from a linked list.

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Donne Martin 2015-05-06 19:15:09 -04:00
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{
"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()"
]
}
],
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"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",
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"nbformat": 4,
"nbformat_minor": 0
}