实现多课程的排序问题，符合先修课程安排的要求，可给出多种排课方案！！本程序的亮点是可得出一组课程的所有可能的拓扑排序,故最终结果是多方案的-Scheduling multi-course meet the requirements of Pre-curriculum can be given a variety of arranging schedule the program! ! The highlight of this program can be drawn from a group of courses in all possible topological sort, so the end result is a multi-program! !