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QueueA.js
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QueueA.js
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/**
* Creates a new queue. A queue is a first-in-first-out (FIFO) data structure -
* items are added to the end of the queue and removed from the front.
*/
function QueueA() {
"use strict";
// initialise the queue and offset
var queue = [],
offset = 0;
/**
* Returns the length of the queue.
*/
this.getLength = function () {
return (queue.length - offset);
};
/**
* Returns true if the queue is empty, and false otherwise.
*/
this.isEmpty = function () {
return (queue.length === 0);
};
/**
* Enqueues the specified item. The parameter is:
* @param {Object} item The item to enqueue
*/
this.enqueue = function (item) {
queue.push(item);
};
/**
* Dequeues an item and returns it. If the queue is empty then undefined is returned.
*/
this.dequeue = function () {
// if the queue is empty, return undefined
if (queue.length === 0) {
return undefined;
}
// store the item at the front of the queue
var item = queue[offset];
// increment the offset and remove the free space if necessary
offset += 1;
if (offset * 2 >= queue.length) {
queue = queue.slice(offset);
offset = 0;
}
// return the dequeued item
return item;
};
/**
* Returns the item at the front of the queue (without dequeuing it). If the
* queue is empty then undefined is returned.
*/
this.peek = function () {
// return the item at the front of the queue
return (queue.length > 0 ? queue[offset] : undefined);
};
}