java - Logic for Grouping number -

i having 1 -10 in different groups a,b , c. eg. a-1,a-2,a-3,b-4,c-5,b-6,a-7,c-8,a-9,a,10

i want make group separately a, b , c

a 1-3, 7, 9-10  b 4, 6  c 5, 8 

can 1 me logic..?

guava creating data structure need:

public static void main(final string[] args) {     string input = "a-1,a-2,a-3,b-4,c-5,b-6,a-7,c-8,a-9,a-10";      // create multimap     map<string, collection<integer>> map=maps.newtreemap();     sortedsetmultimap<string, integer> multimap = multimaps.newsortedsetmultimap(         map, new supplier<sortedset<integer>>() {           public sortedset<integer> get() {               return new treeset<integer>();           }     });      //add data     splitter entrysplitter = splitter.on(',');     splitter keyvaluesplitter = splitter.on('=');     (string entry : entrysplitter.split(input)) {         iterator<string> tokens = keyvaluesplitter.split(entry).iterator();         multimap.put(tokens.next(), integer.valueof(tokens.next()));     }      // read data     (entry<string, collection<integer>> entry : map.entryset()) {         system.out.println(entry.getkey()+":");         printmergedvalues(entry.getvalue());     }  }  private static void printmergedvalues(collection<integer> value) {     // todo implement } 

the thing left join groups