说明：  本程序为使用克鲁斯卡尔 (kruskal)算法构造最小生成树，首先使用链表建立连通图，交换权值以及头和尾，对权值进行排序，使用克鲁斯卡尔 (kruskal)算法构造最小生成树
(This procedure for the use of Kruskal (kruskal) Minimum Spanning Tree Algorithm, the first to use linked lists to establish connectivity map, the right to exchange value, as well as head and tail, sort of weights, the use of Kruskal (kruskal) algorithm for the smallest structure Spanning Tree)