long quick_sort(item_t * A, const int & n)
{
  // base case
  if (1 == n) return 0;
  long counter = 0;
  // choose pivot
  set_pivot_at_beginning(A, n);
  // partition around pivot: assumes pivot is at the beginning
  const int pivot_idx = partition(A, n);
  const int lsize = pivot_idx;
  const int rsize = n - pivot_idx - 1;
  counter += lsize + rsize;
  // sort left and right around pivot
  if(lsize > 0) {
    counter += quick_sort(A, lsize) ;
  }
  if(rsize > 0) {
    counter += quick_sort(A + pivot_idx + 1, rsize) ;
  }
  return counter;
}