这是由VS2013写的一道acm测试题，就是判断有向图是否可以用拓扑排序。如果是拓扑排序，就输出拓扑序列，如果不是，则输出有向图里的自环或者圈。-This is a acm VS2013 written test questions, is to determine whether you can use a directed graph topological sorting. If it is topological sorting, the output sequence topology