广度优先 Given a graph G=(V,E)and a disting 一定是棵树 adth-first search systematically explores the edges of 吗？ ex that is reachable from s.It computes the distance (sm number of edges)from s to each reachable vertex.It also produces a"breadth-first tree"with roots that contains all reachable vertices.For any vertex v reachable from s,the simple path in the breadth-first tree from s to v corresponds to a"shortest path"from s tov in G,that is,a path containing the smallest number of edges.algorithm works on both directed and undirected graphs. 定最短吗？ 显然？广度优先 一定是棵树 吗？ 一定最短吗？ 显然？