updatablepriorityqueue v0.1.3

UpdatablePriorityQueue.js : a updatable heap-based priority queue in

JavaScript based on FastPriorityQueue.js

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.

In an UpdatablePriorityQueue, you can also lookup/modify the elements inside the queue (ie you don't have to interact only with the least-element at the top), at the expense of maintaining some extra state (a mapping from element -> heap-position). After any updates, the priority-queue rebalances.

License: Apache License 2.0

Usage

var x = new UpdatablePriorityQueue();
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 compound object with a functions to extract key and value

var getKey = function (o) { return (o.k); };
var getValue = function (o) { return (o.v); };
var x = new UpdatablePriorityQueue(getKey, getValue);
x.add({'k':'a','v':1,'data':'foo'});
x.add({'k':'b','v':0,'data':'bar'});
x.add({'k':'c','v':5,'data':'baz'});
x.add({'k':'d','v':4,'data':'thud'});
x.add({'k':'e','v':3,'data':'blah'});
while(!x.isEmpty()) {
  console.log(x.poll().data);
} // will print bar foo blah thud baz

You can also update and delete the objects in-place

var getKey = function (o) { return (o.k); };
var getValue = function (o) { return (o.v); };
var x = new UpdatablePriorityQueue(getKey, getValue);
x.add({'k':'a','v':1,'data':'foo'});
x.add({'k':'b','v':0,'data':'bar'});
x.add({'k':'c','v':5,'data':'baz'});
x.add({'k':'d','v':4,'data':'thud'});
x.add({'k':'e','v':3,'data':'blah'});
x.updateElement('e', {'k':'e','v':7,'data':'last'});
x.deleteElement('d');
while(!x.isEmpty()) {
  console.log(x.poll().data);
} // will print bar foo baz last

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

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

npm install

  $ npm install updatablepriorityqueue

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. Update should have complexity roughly equivalent to add.

Testing

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

  $ npm install mocha
  $ npm test