code: public static void sort(IRingSet ringSet) {
          List<IRing> ringList = new ArrayList<IRing>();
          for (IAtomContainer atomContainer : ringSet.atomContainers()) {
              ringList.add((IRing) atomContainer);
          }
          Collections.sort(ringList, new RingSizeComparator(RingSizeComparator.SMALL_FIRST));
          ringSet.removeAllAtomContainers();
          for (IAtomContainer aRingList : ringList)
              ringSet.addAtomContainer(aRingList);
  
      }
docs: Sorts the rings in the set by size. The smallest ring comes
  first.
  @param ringSet The collection of rings