public static void serilize(UndirectedGraphNode x)
    {
        if(x == null) return;
        set.add(x);
        System.out.print(x.label);
        if(x.neighbors == null ||x.neighbors.size() == 0) {System.out.print("#");return;}
        else
        {
            for(UndirectedGraphNode s:x.neighbors) System.out.print(","+s.label);
            System.out.print("#");
        }
        for(UndirectedGraphNode ss:x.neighbors) if(!set.contains(ss)) serilize(ss);
    }