ngraph.path/a-star/NodeHeap.js

/**
 * Based on https://github.com/mourner/tinyqueue
 * Copyright (c) 2017, Vladimir Agafonkin https://github.com/mourner/tinyqueue/blob/master/LICENSE
 * 
 * Adapted for PathFinding needs by @anvaka
 * Copyright (c) 2017, Andrei Kashcha
 */
module.exports = NodeHeap;

function NodeHeap(data, options) {
  if (!(this instanceof NodeHeap)) return new NodeHeap(data, options);

  if (!Array.isArray(data)) {
    // assume first argument is our config object;
    options = data;
    data = [];
  }

  options = options || {};

  this.data = data || [];
  this.length = this.data.length;
  this.compare = options.compare || defaultCompare;
  this.setNodeId = options.setNodeId || noop;

  if (this.length > 0) {
    for (var i = (this.length >> 1); i >= 0; i--) this._down(i);
  }

  if (options.setNodeId) {
    for (var i = 0; i < this.length; ++i) {
      this.setNodeId(this.data[i], i);
    }
  }
}

function noop() {}

function defaultCompare(a, b) {
  return a - b;
}

NodeHeap.prototype = {

  push: function (item) {
    this.data.push(item);
    this.setNodeId(item, this.length);
    this.length++;
    this._up(this.length - 1);
  },

  pop: function () {
    if (this.length === 0) return undefined;

    var top = this.data[0];
    this.length--;

    if (this.length > 0) {
      this.data[0] = this.data[this.length];
      this.setNodeId(this.data[0], 0);
      this._down(0);
    }
    this.data.pop();

    return top;
  },

  peek: function () {
    return this.data[0];
  },

  updateItem: function (pos) {
    this._down(pos);
    this._up(pos);
  },

  _up: function (pos) {
    var data = this.data;
    var compare = this.compare;
    var setNodeId = this.setNodeId;
    var item = data[pos];

    while (pos > 0) {
      var parent = (pos - 1) >> 1;
      var current = data[parent];
      if (compare(item, current) >= 0) break;
        data[pos] = current;

       setNodeId(current, pos);
       pos = parent;
    }

    data[pos] = item;
    setNodeId(item, pos);
  },

  _down: function (pos) {
    var data = this.data;
    var compare = this.compare;
    var halfLength = this.length >> 1;
    var item = data[pos];
    var setNodeId = this.setNodeId;

    while (pos < halfLength) {
      var left = (pos << 1) + 1;
      var right = left + 1;
      var best = data[left];

      if (right < this.length && compare(data[right], best) < 0) {
        left = right;
        best = data[right];
      }
      if (compare(best, item) >= 0) break;

      data[pos] = best;
      setNodeId(best, pos);
      pos = left;
    }

    data[pos] = item;
    setNodeId(item, pos);
  }
};