[POJ 2762]Going from u to v or from v to u? (强连通分量+拓扑排序)
DescriptionInordertomaketheirsonsbrave,JiajiaandWindtakethemtoabigcave.Thecavehasnrooms,andone-waycorridorsconnectingsomerooms.Eachtime,Windchoosetworoomsxandy,andaskoneoftheirlittlesonsgofromonetothe