Problem:
 Input: a non-directed graph G
 Output: a list of list of nodes representing the connected components
  of G (each inner list is a connected component)

ConnectedComponents(G)
   res = CreateEmptyList()
   for each v in Vertices(G)
      if not(marked(v)) then
         l = CreateEmptyList()
         VisitComponent(G,v,l)
         res.push(l)
   return res


VisitComponet(G,v,l)
   l.push(v)
   mark(v)
   for each w in AdjSet(v)
      if not(marked(w)) then
         VisitComponent(G,w,l)


Code practically identical to DFS, but for
print than becomes l.push() (which is O(1))

Thus, same complexity as DFS, i.e. O(#E + #V) in case
of adjacency lists/sets.