Box Relations //2009 Asia Wuhan Regional Contest Hosted by Wuhan University 拓扑排序
BoxRelationsTimeLimit:2000/1000MS(Java/Others) MemoryLimit:32768/32768K(Java/Others)TotalSubmission(s):301 AcceptedSubmission(s):94SpecialJudgeProblemDescriptionThereare n boxes C1,C2,...,Cn in3