说明：  关键路径通常是在拓扑排序的基础上求得的。本文算法中设计了一些独特的数据结构，在算法运行的整个 过程中，求发点(源点)到收点(终点)的关键路径的过程(入栈、出栈等操作)实际只进行一遍，不需要进行拓扑排序，算法的时间 复杂度为O(n+e)，较传统的算法效率更高
(Critical path is usually calculated based on the topological sort of. This algorithm designed some unique data structure, algorithm running throughout the process, find the starting point (source) to the resumption point (end point) the critical path of the process (stack, the stack, etc. operations) actually only one set , does not require the topological sort algorithm time complexity is O (n+ e), the algorithm is more efficient than traditional)