输入事例：
7 9
1 2 28
1 6 10
2 3 16
2 7 14
3 4 12
4 5 22
4 7 18
5 6 25
5 7 24
输出：
1 6 10
6 5 25
5 4 22
4 3 12
3 2 16
2 7 14
weight if MST is 99
1 #include <cstdio>
2 #include <cstring>
3 #define INF 1000000 //无穷大
4 #define MAXN 21 //顶点个数最大值
5
6 int n, m; //顶点个数、边数
7 int Edge[MAXN][MAXN]; //邻接矩阵
8 int lowcost[MAXN];
9 int nearvex[MAXN];
10
11 void prim( int u0 ) //从顶点u0出发执行普里姆算法
12 {
13 int i, j; //循环变量
14 int sumweight = 0; //生成树的权值
15
16 for( i=1; i<=n; i++ ) //初始化lowcost数组和nearvex数组
17 {
18 lowcost[i] = Edge[u0][i];
19 nearvex[i] = u0;
20 }
21 nearvex[u0] = -1;
22
23 for( i=1; i<n; i++ )
24 {
25 int min = INF;
26 int v = -1;
27 for( j=1; j<=n; j++ ) //在lowcost数组(的nearvex[ ]值为-1的元素中)中找最小值
28 {
29 if( nearvex[j]!=-1 && lowcost[j]<min )
30 { v = j; min = lowcost[j]; }
31 }
32 if( v!=-1 ) //v==-1，表示没找到权值最小的边
33 {
34 printf( "%d %d %d\n", nearvex[v], v, lowcost[v] );
35 nearvex[v] = -1;
36 sumweight += lowcost[v];
37
38 for( j=1; j<=n; j++ )
39 {
40 if( nearvex[j]!=-1 && Edge[v][j]<lowcost[j] )
41 {
42 lowcost[j] = Edge[v][j];
43 nearvex[j] = v;
44 }
45 }
46 }//end of if
47 }//end of for
48 printf( "weight of MST is %d\n", sumweight );
49 }//end of prime
50
51 int main( )
52 {
53 int i, j; //循环变量
54 int u, v, w; //边的起点和终点及权值
55 scanf( "%d%d", &n, &m ); //读入顶点个数n和边数m
56 memset( Edge, 0, sizeof(Edge) );
57 for( i=1; i<=m; i++ )
58 {
59 scanf( "%d%d%d", &u, &v, &w ); //读入边的起点和终点
60 Edge[u][v] = Edge[v][u] = w; //构造邻接矩阵
61 }
62 for( i=1; i<=n; i++ ) //对邻接矩阵中其他元素值进行赋值
63 {
64 for( j=1; j<=n; j++ )
65 {
66 if( i==j ) Edge[i][j] = 0;
67 else if( Edge[i][j]==0 ) Edge[i][j] = INF;
68 }
69 }
70 prim( 1 ); //从顶点1出发构造最小生成树
71 return 0;
72 }
