说明：  在一个具有几个顶点的连通图G中，如果存在子图G 包含G中所有顶点和一部分边，且不形成回路，则称G 为图G的生成树，代价最小生成树则称为最小生成树。
(Has several vertices in a connected graph G, if there subgraph G ' contains all vertices of G and part of the side, and does not form a loop, called G' is a spanning tree of G, the minimum cost spanning tree is called minimum spanning tree.)