docs: private void permutePivot(IntIntPair pos1, IntIntPair pos2) {
      int r1 = pos1.first;
      int c1 = pos1.second;
      int r2 = pos2.first;
      int c2 = pos2.second;
      int index;
      index = row[r2];
      row[r2] = row[r1];
      row[r1] = index;
      index = col[c2];
      col[c2] = col[c1];
      col[c1] = index;
    }