说明：  Dandn文件给出了输入参数的名称及格式 即在调用prim前先输入邻接矩阵D和节点个数n 输入prim 得到两行的矩阵T,将上下两行数字对应的节点相连即可
(The dandn file gives the name and format of the input parameters That is, input the adjacency matrix D and the number of nodes n before calling prim Input prim The matrix t of two lines is obtained, and the nodes corresponding to the numbers of the upper and lower lines are connected)