binaryheap.js

module.exports = function(scoreFunction) {
    this.content = [];
    this.scoreFunction = scoreFunction;
}

module.exports.prototype = {
    push: function(element) {
        // Add the new element to the end of the array.
        this.content.push(element);
        // Allow it to sink down.
        this.sinkDown(this.content.length - 1);
    },

    pop: function() {
        // Store the first element so we can return it later.
        var result = this.content[0];
        // Get the element at the end of the array.
        var end = this.content.pop();
        // If there are any elements left, put the end element at the
        // start, and let it bubble up.
        if (this.content.length > 0) {
            this.content[0] = end;
            this.bubbleUp(0);
        }
        return result;
    },
    remove: function(node) {

        var i = this.content.indexOf(node);

        // When it is found, the process seen in 'pop' is repeated
        // to fill up the hole.
        var end = this.content.pop();
        if (i != this.content.length - 1) {
            this.content[i] = end;
            if (this.scoreFunction(end) < this.scoreFunction(node)) this.sinkDown(i);
            else
            this.bubbleUp(i);
        }
    },

    size: function() {
        return this.content.length;
    },

    rescoreElement: function(node) {
        this.sinkDown(this.content.indexOf(node));
    },
    sinkDown: function(n) {
        // Fetch the element that has to be sunk.
        var element = this.content[n];
        // When at 0, an element can not sink any further.
        while (n > 0) {
            // Compute the parent element's index, and fetch it.
            var parentN = ((n + 1) >> 1) - 1,
                parent = this.content[parentN];
            // Swap the elements if the parent is greater.
            if (this.scoreFunction(element) < this.scoreFunction(parent)) {
                this.content[parentN] = element;
                this.content[n] = parent;
                // Update 'n' to continue at the new position.
                n = parentN;
            }
            // Found a parent that is less, no need to sink any further.
            else {
                break;
            }
        }
    },

    bubbleUp: function(n) {
        // Look up the target element and its score.
        var length = this.content.length,
            element = this.content[n],
            elemScore = this.scoreFunction(element);

        while (true) {
            // Compute the indices of the child elements.
            var child2N = (n + 1) << 1,
                child1N = child2N - 1;
            // This is used to store the new position of the element,
            // if any.
            var swap = null;
            // If the first child exists (is inside the array)...
            if (child1N < length) {
                // Look it up and compute its score.
                var child1 = this.content[child1N],
                    child1Score = this.scoreFunction(child1);
                // If the score is less than our element's, we need to swap.
                if (child1Score < elemScore) swap = child1N;
            }
            // Do the same checks for the other child.
            if (child2N < length) {
                var child2 = this.content[child2N],
                    child2Score = this.scoreFunction(child2);
                if (child2Score < (swap == null ? elemScore : child1Score)) swap = child2N;
            }

            // If the element needs to be moved, swap it, and continue.
            if (swap != null) {
                this.content[n] = this.content[swap];
                this.content[swap] = element;
                n = swap;
            }
            // Otherwise, we are done.
            else {
                break;
            }
        }
    }
};