DES tree: directed Ime W W 1/8Q92 2/7 Z 3/6 ees 2/32021 Xiaojuan CaiDFS tree: directed u w x y z u u u v v x y w z y x DFS trees w z time = 0 1/ 2/ 3/ 4/5 6 7 8 9/ 10/ 11 12 2/3/2021 Xiaojuan Cai 31