Created
September 23, 2012 02:08
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Javascript Priority Queue Implementation
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//Constants | |
PriorityQueue.MAX_HEAP = 0; | |
PriorityQueue.MIN_HEAP = 1; | |
/** | |
* This is an improved Priority Queue data type implementation that can be used to sort any object type. | |
* It uses a technique called a binary heap. | |
* | |
* For more on binary heaps see: http://en.wikipedia.org/wiki/Binary_heap | |
* | |
* @param criteria The criteria by which to sort the objects. This should be a property of the objects you're sorting. | |
* @param heapType either PriorityQueue.MAX_HEAP or PriorityQueue.MIN_HEAP. | |
**/ | |
function PriorityQueue(criteria,heapType) { | |
this.length = 0; //The current length of heap. | |
var queue = []; | |
var isMax = false; | |
//Constructor | |
if (heapType==PriorityQueue.MAX_HEAP) { | |
isMax = true; | |
} else if (heapType==PriorityQueue.MIN_HEAP) { | |
isMax = false; | |
} else { | |
throw heapType + " not supported."; | |
} | |
/** | |
* Inserts the value into the heap and sorts it. | |
* | |
* @param value The object to insert into the heap. | |
**/ | |
this.insert = function(value) { | |
if (!value.hasOwnProperty(criteria)) { | |
throw "Cannot insert " + value + " because it does not have a property by the name of " + criteria + "."; | |
} | |
queue.push(value); | |
length++; | |
bubbleUp(length-1); | |
} | |
/** | |
* Peeks at the highest priority element. | |
* | |
* @return the highest priority element | |
**/ | |
this.getHighestPriorityElement = function() { | |
return queue[0]; | |
} | |
/** | |
* Removes and returns the highest priority element from the queue. | |
* | |
* @return the highest priority element | |
**/ | |
this.shiftHighestPriorityElement = function() { | |
if (length < 0) { | |
throw ("There are no more elements in your priority queue."); | |
} | |
var oldRoot = queue[0]; | |
var newRoot = _queue.pop(); | |
length--; | |
queue[0] = newRoot; | |
swapUntilQueueIsCorrect(0); | |
return oldRoot; | |
} | |
var bubbleUp = function(index) { | |
if (index==0) { | |
return; | |
} | |
var parent = getParentOf(index); | |
if (evaluate(index,parent)) { | |
swap(index,parent); | |
bubbleUp(parent); | |
} else { | |
return; | |
} | |
} | |
var swapUntilQueueIsCorrect = function(value) { | |
left = getLeftOf(value); | |
right = getRightOf(value); | |
if (evaluate(left,value)) { | |
swap(value,left); | |
swapUntilQueueIsCorrect(left); | |
} else if (evaluate(right,value)) { | |
swap(value,right); | |
swapUntilQueueIsCorrect(right); | |
} else if (value==0) { | |
return; | |
} else { | |
swapUntilQueueIsCorrect(0); | |
} | |
} | |
var swap = function(self,target) { | |
var placeHolder = queue[self]; | |
queue[self] = queue[target]; | |
queue[target] = placeHolder; | |
} | |
/* | |
/*Helpers | |
*/ | |
var evaluate = function(self,target) { | |
if (queue[target]==null||queue[self]==null) { | |
return false; | |
} | |
if (isMax) { | |
if (queue[self][criteria] > queue[target][criteria]) { | |
return true; | |
} else { | |
return false; | |
} | |
} else { | |
if (queue[self][criteria] < queue[target][criteria]) { | |
return true; | |
} else { | |
return false; | |
} | |
} | |
} | |
var getParentOf = function(index) { | |
return Math.floor(index/2)-1; | |
} | |
var getLeftOf = function(index) { | |
return index*2 + 1; | |
} | |
var getRightOf = function(index) { | |
return index*2 + 2; | |
} | |
} |
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hello, have to put this.length in lines:
38 39 57 62
:)