问题 M: Playing Tag on Tree------------------------------思维(图论)
题目描述WehaveatreewithNvertices.Thei-thedgeconnectsVertexAiandBibidirectionally.TakahashiisstandingatVertexu,andAokiisstandingatVertexv.Now,theywillplayagameoftagasfollows:IfTakahashiandAokiarestandingat