int findMinChild(int index) {
      return findMin(getLeftChildIndex(index), 2);
    }

    /** Returns the minimum grand child or -1 if no grand child exists. */
    int findMinGrandChild(int index) {
      int leftChildIndex = getLeftChildIndex(index);
      if (leftChildIndex < 0) {
        return -1;
      }
      return findMin(getLeftChildIndex(leftChildIndex), 4);
    }

    /**