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/*
Queue.js
A function to represent a queue
Created by Kate Morley - http://code.iamkate.com/ - and released under the terms
of the CC0 1.0 Universal legal code:
http://creativecommons.org/publicdomain/zero/1.0/legalcode
*/
var MAX_UNUSED_ARRAY_SIZE = 10000
/* 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 Queue() {
// initialise the queue and offset
var queue = []
var offset = 0
// Returns the length of the queue.
this.getLength = function () {
return (queue.length - offset)
}
/* Enqueues the specified item. The parameter is:
*
* item - the item to enqueue
*/
this.enqueue = function (item) {
queue.push(item)
}
/* Dequeues an item and returns it. If the queue is empty, the value
* 'undefined' is returned.
*/
this.dequeue = function () {
// if the queue is empty, return immediately
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
if (++offset > MAX_UNUSED_ARRAY_SIZE) {
queue = queue.slice(offset)
offset = 0
}
// return the dequeued item
return item
}
}
module.exports = Queue
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