83 lines
2.0 KiB
JavaScript
83 lines
2.0 KiB
JavaScript
/*
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Queue.js
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A function to represent a queue
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Created by Stephen Morley - http://code.stephenmorley.org/ - and released under
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the terms of the CC0 1.0 Universal legal code:
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http://creativecommons.org/publicdomain/zero/1.0/legalcode
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*/
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/* Creates a new queue. A queue is a first-in-first-out (FIFO) data structure -
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* items are added to the end of the queue and removed from the front.
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*/
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function Queue(){
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// initialise the queue and offset
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var queue = [];
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var offset = 0;
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// Returns the length of the queue.
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this.getLength = function(){
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return (queue.length - offset);
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}
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// Returns true if the queue is empty, and false otherwise.
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this.isEmpty = function(){
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return (queue.length == 0);
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}
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/* Enqueues the specified item. The parameter is:
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*
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* item - the item to enqueue
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*/
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this.enqueue = function(item){
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queue.push(item);
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}
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/* Dequeues an item and returns it. If the queue is empty, the value
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* 'undefined' is returned.
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*/
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this.dequeue = function(){
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// if the queue is empty, return immediately
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if (queue.length == 0) return undefined;
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// store the item at the front of the queue
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var item = queue[offset];
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// increment the offset and remove the free space if necessary
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if (++ offset * 2 >= queue.length){
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queue = queue.slice(offset);
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offset = 0;
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}
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// return the dequeued item
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return item;
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}
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/* Returns the item at the front of the queue (without dequeuing it). If the
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* queue is empty then undefined is returned.
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*/
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this.peek = function(){
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return (queue.length > 0 ? queue[offset] : undefined);
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}
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/* Returns the item at the spot specified by place in the queue (without
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* dequeuing it). If the queue is emprty or the requested place is outside
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* the queue then undefined is returned.
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*/
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this.get = function(place){
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var item = undefined;
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if (queue.length > 0 && place < (queue.length - offset) && place >= 0) {
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item = queue[(offset + place)];
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}
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return item;
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}
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}
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