Introduction - If you have any usage issues, please Google them yourself
2, breadth-first search graph traversal algorithm: First visit to the designated start vertex V0, starting from V0, V0 visit was not visited all the vertices adjacent to W1, W2 ... ..., Wk, and then followed from the W1, W2 ... ..., Wk, the visit they all have not been visited adjacent vertex, and so on, until the map has not been visited by all adjacent vertices have been visited so far.