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
(Dandn file name given input parameters and format that is called prim before Input adjacency matrix D and node numbers n input prim are two lines of the matrix T, the number of up and down two lines can be connected to the corresponding node)