DES tree: undirected 1/6Q 9 How to figure out back edges 2/5 o tree edge back edge W 4/10 DES tree 2/32021 Xiaojuan CaiDFS tree: undirected • tree edge: • back edge: u v x y w z DFS tree 1/ 2/ 3/ 4/1 4 5 6 5/ 6/2 3 2/3/2021 Xiaojuan Cai 13 How to figure out back edges?