如果以无向网表示N个城市之间通信网络的建设计划，顶点表示城市，边上的权表示该线路的造价，设计一个方案，使这个通信网的总造价最低。

-If no N to the network that communication networks between cities, building plans, vertex, said the city, the right side of the line that the cost to design a program to make this the lowest total cost of communication networks.