> 0) {
        threshold = buffer[i];
      }
    }
  }

  /**
   * Partitions the contents of buffer in the range [left, right] around the pivot element
   * previously stored in buffer[pivotValue]. Returns the new index of the pivot element,
   * pivotNewIndex, so that everything in [left, pivotNewIndex] is ≤ pivotValue and everything in
   * (pivotNewIndex, right] is greater than pivotValue.
   */