docs: private static void quickSort(/*@non_null@*/ double[] array, /*@non_null@*/ int[] index, 
                                  int left, int right) {
  
      if (left < right) {
        int middle = partition(array, index, left, right);
        quickSort(array, index, left, middle);
        quickSort(array, index, middle + 1, right);
      }
    }