code: private static <T extends Comparable<? super T>> void heapify(T[] arr) {
          int n = arr.length;
          for (int i = n / 2 - 1; i >= 0; i--)
              SortUtils.siftDown(arr, i, n - 1);
      }
docs: Place the array in max-heap order. Note that the array is not fully sorted.