83 lines
2.0 KiB
JavaScript
83 lines
2.0 KiB
JavaScript
/*
|
|
|
|
Queue.js
|
|
|
|
A function to represent a queue
|
|
|
|
Created by Stephen Morley - http://code.stephenmorley.org/ - and released under
|
|
the terms of the CC0 1.0 Universal legal code:
|
|
|
|
http://creativecommons.org/publicdomain/zero/1.0/legalcode
|
|
|
|
*/
|
|
|
|
/* 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);
|
|
}
|
|
|
|
// Returns true if the queue is empty, and false otherwise.
|
|
this.isEmpty = function(){
|
|
return (queue.length == 0);
|
|
}
|
|
|
|
/* 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 * 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 (queue.length > 0 ? queue[offset] : undefined);
|
|
}
|
|
|
|
/* Returns the item at the spot specified by place in the queue (without
|
|
* dequeuing it). If the queue is emprty or the requested place is outside
|
|
* the queue length then undefined is returned.
|
|
*/
|
|
this.get = function(place){
|
|
var item = undefined;
|
|
if (queue.length > 0 && place < (queue.length - offset)) {
|
|
item = queue[(offset + place)];
|
|
}
|
|
return item;
|
|
}
|
|
|
|
}
|