p.612: 22.3-12 Show that a depth-first search of an undirected graph G can be used to identify the connected components of G, and that the depth-first forest contains as many trees as G has connected components. More precisely, show how to modify depth-first search so that each vertex v is assigned an integer label cc[y] between l and k, where k is the number of connected components of G, such that ccfu]=cc[v] if and only if u and v are in the same connected component