堆排序

var heapSort = function(arr) {
  buildMaxHeap(arr);
  for (var i = arr.length - 1; i > 0; i--) {
    swap(arr, 0, i);
    maxHeapify(arr, 0, i);
  }
};

var buildMaxHeap = function(arr) {
  for (var i = (arr.length / 2 | 0) - 1; i >= 0; i--) {
    maxHeapify(arr, i, arr.length);
  }
};

var maxHeapify = function(arr, i, size) {
  var l = 2 * i + 1,
      r = l + 1,
      maxIndex = i;
  
  if (l < size && arr[l] > arr[maxIndex]) {
    maxIndex = l;
  }

  if (r < size && arr[r] > arr[maxIndex]) {
    maxIndex = r;
  }

  if (maxIndex !== i) {
    swap(arr, i, maxIndex);
    maxHeapify(arr, maxIndex, size);
  }
};

var swap = function(a, i, j) {
  var t = a[i];
  a[i] = a[j];
  a[j] = t;
};