拓扑排序：对给定的AOV网判断网中是否存在环，检测的办法是对有向图构造其顶点的拓扑有序序列，若网中所有顶点都在它的拓扑有序序列中，则该AOV网中必定不存在环。在拓扑排序的基础上实现关键路径的的求解。-Topological Sort: AOV of a given network to determine the existence of ring network to detect the approach is the directed graph topological structure of its vertices in an orderly sequence, if all vertex network topology in its orderly sequence, the AOV network does not exist is bound to ring. In the topological sort on the basis of solving the critical path.