LCA recent public ancestor Tarjan offline algorithm

Study Blog: http://noalgo.info/476.html speak very clearly!

For a tree, the DFS traversal is traversed first, and the collection of the current and parent nodes is maintained using and checking the set. So if the association node (B) of the current node (a) (and another point of the nearest ancestor requested) has been accessed before, then

B can already belong to a set, previously for the point of access, has maintained the root of the collection of that point, so find the root of the collection where the B node is located, then this point is the nearest root, because of the order of DFS access.

LCA recent public ancestor Tarjan offline algorithm