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Nicholas C. Zakas
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Classic implementation of a linked list that doesn't store length
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‎data-structures/linked-list-classic/linked-list-classic-tests.htm‎

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<html>
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<head>
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<title>Linked List Tests</title>
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<!-- Combo-handled YUI CSS files: -->
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<link rel="stylesheet" type="text/css" href="http://yui.yahooapis.com/combo?2.7.0/build/logger/assets/logger.css&2.7.0/build/yuitest/assets/testlogger.css">
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<!-- Combo-handled YUI JS files: -->
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<script type="text/javascript" src="http://yui.yahooapis.com/combo?2.7.0/build/yahoo-dom-event/yahoo-dom-event.js&2.7.0/build/logger/logger-min.js&2.7.0/build/yuitest/yuitest-min.js"></script>
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<script type="text/javascript" src="linked-list-classic.js"></script>
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</head>
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<body>
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<h1>Linked List Tests</h1>
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<script type="text/javascript">
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YAHOO.namespace("test");
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YAHOO.test.LinkedList = (function(){
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var assert = YAHOO.util.Assert;
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//-------------------------------------------------------------------------
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// Base Test Suite
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//-------------------------------------------------------------------------
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var suite = new YAHOO.tool.TestSuite("Linked List Tests");
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//-------------------------------------------------------------------------
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// Test Case for adding
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//-------------------------------------------------------------------------
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suite.add(new YAHOO.tool.TestCase({
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name : "add() Tests",
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setUp: function(){
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this.list = new LinkedList();
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},
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tearDown: function(){
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delete this.list;
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},
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//---------------------------------------------------------------------
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// Tests
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//---------------------------------------------------------------------
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testAddSingle: function(){
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this.list.add("Hi");
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assert.areEqual(1, this.list.size(), "List should have one item.");
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assert.areEqual("Hi", this.list._head.data, "First item should have data of 'Hi'.");
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assert.isNull(this.list._head.next, "The next pointer of the first item should be null.");
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},
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testAddMultiple: function(){
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this.list.add("Hi");
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this.list.add("Yo");
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assert.areEqual(2, this.list.size(), "List should have one item.");
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assert.areEqual("Hi", this.list._head.data, "First item should have data of 'Hi'.");
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assert.isNull(this.list._head.next.next, "The next pointer of the second item should be null.");
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}
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}));
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//-------------------------------------------------------------------------
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// Test Case for retrieving values
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//-------------------------------------------------------------------------
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suite.add(new YAHOO.tool.TestCase({
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name : "item() Tests",
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setUp: function(){
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this.list = new LinkedList();
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this.list.add("Hi");
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this.list.add("Yo");
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this.list.add("Bye");
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},
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tearDown: function(){
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delete this.list;
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},
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//---------------------------------------------------------------------
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// Tests
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//---------------------------------------------------------------------
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testGetFirstItem: function(){
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var value = this.list.item(0);
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assert.areEqual("Hi", value, "First item should be 'Hi'.");
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},
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testGetMiddleItem: function(){
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var value = this.list.item(1);
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assert.areEqual("Yo", value, "Second item should be 'Yo'.");
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},
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testGetLastItem: function(){
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var value = this.list.item(2);
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assert.areEqual("Bye", value, "Second item should be 'Bye'.");
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},
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testGetInvalidItem: function(){
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var value = this.list.item(5);
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assert.isNull(value, "Invalid items should return null.");
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},
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}));
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//-------------------------------------------------------------------------
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// Test Case for removing values
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//-------------------------------------------------------------------------
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suite.add(new YAHOO.tool.TestCase({
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name : "remove() Tests",
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setUp: function(){
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this.list = new LinkedList();
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this.list.add("Hi");
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this.list.add("Yo");
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this.list.add("Bye");
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},
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tearDown: function(){
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delete this.list;
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},
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//---------------------------------------------------------------------
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// Tests
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//---------------------------------------------------------------------
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testRemoveFirstItem: function(){
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var value = this.list.remove(0);
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assert.areEqual("Hi", value, "Removed item should be 'Hi'.");
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assert.areEqual(2, this.list.size(), "There should only be two items left.");
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assert.areEqual("Yo", this.list.item(0), "First item should now be 'Yo'.");
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assert.areEqual("Bye", this.list.item(1), "Last item should now be 'Bye'.");
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assert.isNull(this.list.item(2), "Item in position 2 should be null.");
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},
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testRemoveMiddleItem: function(){
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var value = this.list.remove(1);
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assert.areEqual("Yo", value, "Removed item should be 'Yo'.");
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assert.areEqual(2, this.list.size(), "There should only be two items left.");
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assert.areEqual("Hi", this.list.item(0), "First item should now be 'Yo'.");
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assert.areEqual("Bye", this.list.item(1), "Last item should now be 'Bye'.");
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assert.isNull(this.list.item(2), "Item in position 2 should be null.");
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},
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testRemoveLastItem: function(){
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var value = this.list.remove(2);
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assert.areEqual("Bye", value, "Removed item should be 'Bye'.");
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assert.areEqual(2, this.list.size(), "There should only be two items left.");
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assert.areEqual("Hi", this.list.item(0), "First item should now be 'Hi'.");
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assert.areEqual("Yo", this.list.item(1), "Last item should now be 'Yo'.");
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assert.isNull(this.list.item(2), "Item in position 2 should be null.");
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}
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}));
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//-------------------------------------------------------------------------
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// Test Case for converting to an array
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//-------------------------------------------------------------------------
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suite.add(new YAHOO.tool.TestCase({
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name : "toArray() Tests",
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setUp: function(){
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this.list = new LinkedList();
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},
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tearDown: function(){
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delete this.list;
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},
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//---------------------------------------------------------------------
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// Tests
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//---------------------------------------------------------------------
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testToArrayForEmptyList: function(){
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var value = this.list.toArray();
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assert.isInstanceOf(Array, value, "Value should be an array.");
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assert.areEqual(0, value.length, "Array should be empty.");
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},
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testToArrayForOneItemList: function(){
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this.list.add("Hi");
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var value = this.list.toArray();
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assert.isInstanceOf(Array, value, "Value should be an array.");
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assert.areEqual(1, value.length, "Array should have 1 item.");
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assert.areEqual("Hi", value[0], "The only item should be 'Hi'.");
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},
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testToArrayForTwoItemList: function(){
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this.list.add("Hi");
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this.list.add("Yo");
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var value = this.list.toArray();
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assert.isInstanceOf(Array, value, "Value should be an array.");
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assert.areEqual(2, value.length, "Array should have 2 items.");
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assert.areEqual("Hi", value[0], "The first item should be 'Hi'.");
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assert.areEqual("Yo", value[1], "The second item should be 'Yo'.");
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}
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}));
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//return it
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return suite;
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})();
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(function (){
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//create the logger
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var logger = new YAHOO.tool.TestLogger();
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//add the tests
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YAHOO.tool.TestRunner.add(YAHOO.test.LinkedList);
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YAHOO.tool.TestRunner.run();
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})();
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</script>
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</body>
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</html>

‎data-structures/linked-list-classic/linked-list-classic.js‎

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/*
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* Linked List implementation in JavaScript
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* Copyright (c) 2009 Nicholas C. Zakas
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* MIT Licensed - see LICENSE for details on license.
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*/
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/**
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* A linked list implementation in JavaScript. This is a more "classic"
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* approach that doesn't keep track of the number of items in the list
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* and instead calculates the size when necessary.
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* @class LinkedList
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* @constructor
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*/
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function LinkedList() {
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/**
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* Pointer to first item in the list.
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* @property _head
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* @type Object
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* @private
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*/
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this._head = null;
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}
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LinkedList.prototype = {
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//restore constructor
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constructor: LinkedList,
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/**
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* Appends some data to the end of the list. This method traverses
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* the existing list and places the value at the end in a new item.
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* @param {variant} data The data to add to the list.
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* @return {Void}
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* @method add
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*/
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add: function (data){
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//create a new item object, place data in
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var node = {
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data: data,
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next: null
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},
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//used to traverse the structure
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current;
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//special case: no items in the list yet
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if (this._head === null){
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this._head = node;
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} else {
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current = this._head;
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while(current.next){
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current = current.next;
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}
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current.next = node;
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}
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},
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/**
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* Retrieves the data in the given position in the list.
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* @param {int} index The zero-based index of the item whose value
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* should be returned.
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* @return {variant} The value in the "data" portion of the given item
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* or null if the item doesn't exist.
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* @method item
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*/
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item: function(index){
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//check for out-of-bounds values
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if (index > -1){
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var current = this._head,
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i = 0;
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while(i++ < index && current){
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current = current.next;
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}
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return (current ? current.data : null);
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} else {
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return null;
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}
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},
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/**
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* Removes the item from the given location in the list.
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* @param {int} index The zero-based index of the item to remove.
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* @return {variant} The data in the given position in the list or null if
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* the item doesn't exist.
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* @method remove
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*/
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remove: function(index){
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//check for out-of-bounds values
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if (index > -1){
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var current = this._head,
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previous,
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i = 0;
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//special case: removing first item
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if (index === 0){
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this._head = current.next;
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} else {
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//find the right location
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while(i++ < index){
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previous = current;
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current = current.next;
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}
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//skip over the item to remove
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previous.next = current.next;
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}
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//return the value
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return (current ? current.data : null);
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} else {
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return null;
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}
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},
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/**
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* Returns the number of items in the list.
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* @return {int} The number of items in the list.
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* @method size
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*/
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size: function(){
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var current = this._head,
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count = 0;
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while(current){
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count++;
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current = current.next;
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}
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return count;
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},
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/**
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* Converts the list into an array.
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* @return {Array} An array containing all of the data in the list.
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* @method toArray
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*/
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toArray: function(){
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var result = [],
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current = this._head;
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while(current){
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result.push(current.data);
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current = current.next;
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}
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return result;
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},
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/**
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* Converts the list into a string representation.
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* @return {String} A string representation of the list.
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* @method toString
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*/
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toString: function(){
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return this.toArray().toString();
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}
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};

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