说明：  用Kruskal算法构造最小生成树解决指派问题（assignment problem） 一家公司经理准备安排 名员工去完成 项任务，每人一项。由于各员工的特点不同，不同的员工去完成同一项任务时所获得的回报是不同的。如何分配工作方案可以使总回报最大？
(Kruskal Algorithm used to solve assignment problem minimum spanning tree (assignment problem), a manager of the company prepare arrangements for employees to complete tasks, each one. As a result of the characteristics of different staff, different staff to accomplish the same mission when the return is different. How to allocate the work program can make the greatest total return?)