code: private List<Integer> getAtomNosForRingGroup(IAtomContainer molecule, List<Integer> ringGroup, IRingSet ringSet) {
          List<Integer> atc = new ArrayList<Integer>();
          for (Integer i : ringGroup) {
              for (IAtom atom : ringSet.getAtomContainer(i).atoms()) {
                  if (atc.size() > 0) {
                      if (!atc.contains(molecule.indexOf(atom))) {
                          atc.add(molecule.indexOf(atom));
                      }
                  } else {
                      atc.add(molecule.indexOf(atom));
                  }
              }
          }
          return atc;
      }
docs: Gets the List of atom nos corresponding to a particular set of fused rings.
  
  @param {@link IAtomContainer} molecule
  @param ringGroup
  @param {@link IRingSet} ringSet
  @return List of atom numbers for each set