Number of vertices
n = 6 ; for ( int i = 0 ; i < tree . length ; i ++ ) tree [ i ] = new Vector < Integer > ( ) ; addEdge ( 0 , 1 ) ; addEdge ( 0 , 2 ) ; addEdge ( 1 , 3 ) ; addEdge ( 3 , 4 ) ; addEdge ( 3 , 5 ) ;