/**
 * FastPriorityQueue.js : a fast heap-based priority queue  in JavaScript.
 * (c) the authors
 * Licensed under the Apache License, Version 2.0.
 *
 * Speed-optimized heap-based priority queue for modern browsers and JavaScript engines.
 *
 * Usage :
         Installation (in shell, if you use node):
         $ npm install fastpriorityqueue

         Running test program (in JavaScript):

         // var FastPriorityQueue = require("fastpriorityqueue");// in node
         var x = new FastPriorityQueue();
         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
 */
'use strict';

var defaultcomparator = function(a, b) {
  return a < b;
};

// the provided comparator function should take a, b and return *true* when a < b
function FastPriorityQueue(comparator) {
  if (!(this instanceof FastPriorityQueue)) return new FastPriorityQueue(comparator);
  this.array = [];
  this.size = 0;
  this.compare = comparator || defaultcomparator;
}

FastPriorityQueue.prototype.clone = function() {
  var fpq = new FastPriorityQueue(this.compare);
  fpq.size = this.size;
  for (var i = 0; i < this.size; i++) {
    fpq.array.push(this.array[i]);
  }
  return fpq;
};

// Add an element into the queue
// runs in O(log n) time
FastPriorityQueue.prototype.add = function(myval) {
  var i = this.size;
  this.array[this.size] = myval;
  this.size += 1;
  var p;
  var ap;
  while (i > 0) {
    p = (i - 1) >> 1;
    ap = this.array[p];
    if (!this.compare(myval, ap)) {
      break;
    }
    this.array[i] = ap;
    i = p;
  }
  this.array[i] = myval;
};

// replace the content of the heap by provided array and "heapifies it"
FastPriorityQueue.prototype.heapify = function(arr) {
  this.array = arr;
  this.size = arr.length;
  var i;
  for (i = this.size >> 1; i >= 0; i--) {
    this._percolateDown(i);
  }
};

// for internal use
FastPriorityQueue.prototype._percolateUp = function(i, force) {
  var myval = this.array[i];
  var p;
  var ap;
  while (i > 0) {
    p = (i - 1) >> 1;
    ap = this.array[p];
    // force will skip the compare
    if (!force && !this.compare(myval, ap)) {
      break;
    }
    this.array[i] = ap;
    i = p;
  }
  this.array[i] = myval;
};

// for internal use
FastPriorityQueue.prototype._percolateDown = function(i) {
  var size = this.size;
  var hsize = this.size >>> 1;
  var ai = this.array[i];
  var l;
  var r;
  var bestc;
  while (i < hsize) {
    l = (i << 1) + 1;
    r = l + 1;
    bestc = this.array[l];
    if (r < size) {
      if (this.compare(this.array[r], bestc)) {
        l = r;
        bestc = this.array[r];
      }
    }
    if (!this.compare(bestc, ai)) {
      break;
    }
    this.array[i] = bestc;
    i = l;
  }
  this.array[i] = ai;
};

// internal
// _removeAt(index) will delete the given index from the queue,
// retaining balance. returns true if removed.
FastPriorityQueue.prototype._removeAt = function(index) {
  if (this.isEmpty() || index > this.size - 1 || index < 0) return false;

  // impl1:
  //this.array.splice(index, 1);
  //this.heapify(this.array);
  // impl2:
  this._percolateUp(index, true);
  this.poll();
  return true;
};

// remove(myval[, comparator]) will remove the given item from the
// queue, checked for equality by using compare if a new comparator isn't provided.
// (for exmaple, if you want to remove based on a seperate key value, not necessarily priority).
// return true if removed.
FastPriorityQueue.prototype.remove = function(myval, comparator) {
  if (!comparator) {
    comparator = this.compare;
  }
  if (this.isEmpty()) return false;
  for (var i = 0; i < this.size; i++) {
    if (comparator(this.array[i], myval) || comparator(myval, this.array[i])) {
      continue;
    }
    // items are equal, remove
    return this._removeAt(i);
  }
  return false;
};

// Look at the top of the queue (a smallest element)
// executes in constant time
//
// Calling peek on an empty priority queue returns
// the "undefined" value.
// https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/undefined
//
FastPriorityQueue.prototype.peek = function() {
  if (this.size == 0) return undefined;
  return this.array[0];
};

// remove the element on top of the heap (a smallest element)
// runs in logarithmic time
//
// If the priority queue is empty, the function returns the
// "undefined" value.
// https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/undefined
//
// For long-running and large priority queues, or priority queues
// storing large objects, you may  want to call the trim function
// at strategic times to recover allocated memory.
FastPriorityQueue.prototype.poll = function() {
  if (this.size == 0) return undefined;
  var ans = this.array[0];
  if (this.size > 1) {
    this.array[0] = this.array[--this.size];
    this._percolateDown(0 | 0);
  } else {
    this.size -= 1;
  }
  return ans;
};

// This function adds the provided value to the heap, while removing
//  and returning the peek value (like poll). The size of the priority
// thus remains unchanged.
FastPriorityQueue.prototype.replaceTop = function(myval) {
  if (this.size == 0) return undefined;
  var ans = this.array[0];
  this.array[0] = myval;
  this._percolateDown(0 | 0);
  return ans;
};

// recover unused memory (for long-running priority queues)
FastPriorityQueue.prototype.trim = function() {
  this.array = this.array.slice(0, this.size);
};

// Check whether the heap is empty
FastPriorityQueue.prototype.isEmpty = function() {
  return this.size === 0;
};

// iterate over the items in order, pass a callback that receives (item, index) as args.
// TODO once we transpile, uncomment
// if (Symbol && Symbol.iterator) {
//   FastPriorityQueue.prototype[Symbol.iterator] = function*() {
//     if (this.isEmpty()) return;
//     var fpq = this.clone();
//     while (!fpq.isEmpty()) {
//       yield fpq.poll();
//     }
//   };
// }
FastPriorityQueue.prototype.forEach = function(callback) {
  if (this.isEmpty() || typeof callback != 'function') return;
  var i = 0;
  var fpq = this.clone();
  while (!fpq.isEmpty()) {
    callback(fpq.poll(), i++);
  }
};

// return the k 'smallest' elements of the queue
// runs in O(k log k) time
// this is the equivalent of repeatedly calling poll, but
// it has a better computational complexity, which can be
// important for large data sets.
FastPriorityQueue.prototype.kSmallest = function(k) {
  if (this.size == 0) return [];
  var comparator = this.compare;
  var arr = this.array
  var fpq = new FastPriorityQueue(function(a,b){
   return comparator(arr[a],arr[b]);
  });
  k = Math.min(this.size, k);
  var smallest = new Array(k);
  var j = 0;
  fpq.add(0);
  while (j < k) {
    var small = fpq.poll();
    smallest[j++] = this.array[small];
    var l = (small << 1) + 1;
    var r = l + 1;
    if (l < this.size) fpq.add(l);
    if (r < this.size) fpq.add(r);
  }
  return smallest;
}