code: public void checkAndMarkPlaced(IRingSet rs) {
          IRing ring = null;
          boolean allPlaced = true;
          boolean ringsetPlaced = true;
          for (int i = 0; i < rs.getAtomContainerCount(); i++) {
              ring = (IRing) rs.getAtomContainer(i);
              allPlaced = true;
              for (int j = 0; j < ring.getAtomCount(); j++) {
                  if (!((IAtom) ring.getAtom(j)).getFlag(CDKConstants.ISPLACED)) {
                      allPlaced = false;
                      ringsetPlaced = false;
                      break;
                  }
              }
              ring.setFlag(CDKConstants.ISPLACED, allPlaced);
          }
          rs.setFlag(CDKConstants.ISPLACED, ringsetPlaced);
      }
docs: Walks throught the atoms of each ring in a ring set and marks
  a ring as PLACED if all of its atoms have been placed.
  
  @param   rs  The ringset to be checked