queryRange(leftIndex, rightIndex) {
    if (leftIndex > rightIndex) {
      throw new Error('Left index can not be greater than right one');
    }

    if (leftIndex === 1) {
      return this.query(rightIndex);
    }

    return this.query(rightIndex) - this.query(leftIndex - 1);
  }
Query sum from index leftIndex to rightIndex.

@param  {number} leftIndex
@param  {number} rightIndex
@return {number}