在n个城市间建立通信网络，需架设n-1条线路。求解如何以最低经济代价建设此通信网，这是一个最小生成树问题。要求：（1）利用普利姆算法求网的最小生成树；（2）输出生成树中各边及权值。-The n cities to establish communication between networks, the need to set up n-1 lines. How to solve this at the lowest economic cost of building communications network, which is a minimum spanning tree problem. Requirements: (a) the use of plym algorithm for minimum spanning tree network　(2) the output of each spanning tree edge and weights.