StablePriorityQueue.js

A stable heap-based priority queue in JavaScript

In a priority queue, you can...

• query or remove (poll) the smallest element quickly
• insert elements quickly

In practice, "quickly" often means in logarithmic time (O(log n)).

A heap can be used to implement a priority queue.

StablePriorityQueue is an attempt to implement a priority queue in JavaScript that is stable. That is, when equal values are inserted, it will always poll the oldest of the equal values.

License: Apache License 2.0

Usage

var x = new StablePriorityQueue();
x.add(1);
x.add(0);
x.add(5);
x.add(4);
x.add(3);
x.peek(); // should return 0, leaves x unchanged
x.size; // should return 5, leaves x unchanged
while(!x.isEmpty()) {
  console.log(x.poll());
} // will print 0 1 3 4 5
x.trim(); // (optional) optimizes memory usage

You can also provide the constructor with a comparator function.

var x = new StablePriorityQueue(function(a,b) {return b - a});
x.add(1);
x.add(0);
x.add(5);
x.add(4);
x.add(3);
while(!x.isEmpty()) {
  console.log(x.poll());
} // will print 5 4 3 1 0

or

var x = new StablePriorityQueue(function(a, b) {
      return a.energy - b.energy;
});
[{ name: 'player', energy: 10},
 { name: 'monster1', energy: 10},
 { name: 'monster2', energy: 10},
 { name: 'monster3', energy: 10}
].forEach(function(o){
      x.add(o);
})
while (!x.isEmpty()) {
    console.log(x.poll());
}
// will output:
//{ name: 'player', energy: 10 }
//{ name: 'monster1', energy: 10 }
//{ name: 'monster2', energy: 10 }
//{ name: 'monster3', energy: 10 }

If you are using node.js, you need to import the module:

var StablePriorityQueue = require("stablepriorityqueue");
var b = new StablePriorityQueue();// initially empty
b.add(1);// add the value "1"

npm install

  $ npm install stablepriorityqueue

Computational complexity

The function calls "add" and "poll" have logarithmic complexity with respect to the size of the data structure (attribute size). Looking at the top value is a constant time operation.

Testing

Using node.js (npm), you can test the code as follows...

  $ npm install mocha
  $ npm test

You might also like...

If you like this library, you might also like

• https://github.com/lemire/FastBitSet.js
• https://github.com/lemire/FastPriorityQueue.js