private static Map < String , Set < String > > flatten ( Map < String , Set < String > > data ) { Map < String , Set < String > > territories = new TreeMap <> ( ) ; Set < String > keys = data . keySet ( ) ; for ( String key : keys ) { Set < String > values = flatten ( key , territories , data ) ; territories . put ( key , values ) ; } return territories ; }
Flatten the territory containment hierarchy .