code: public void order() {
          Collections.sort(cells, new Comparator<SortedSet<Integer>>() {
  
              @Override
              public int compare(SortedSet<Integer> cellA, SortedSet<Integer> cellB) {
                  return cellA.first().compareTo(cellB.first());
              }
  
          });
      }
docs: Sort the cells in increasing order.