code: String[] symbolicTypes(final IAtomContainer container) {
          EdgeToBondMap bonds = EdgeToBondMap.withSpaceFor(container);
          int[][] graph = GraphUtil.toAdjList(container, bonds);
          return symbolicTypes(container, graph, bonds, new HashSet<IBond>());
      }
docs: Obtain the MMFF symbolic types to the atoms of the provided structure.
  
  @param container structure representation
  @return MMFF symbolic types for each atom index