1 #include <cstdio>
 2 #include <algorithm>
 3 using namespace std;
 4 
 5 int N, M;
 6 
 7 struct Edge{
 8     int u, v, w;
 9     bool operator() (Edge a, Edge b)
10     {
11         return a.w<b.w;
12     }
13 };
14 Edge e[5050];
15 int f[105];
16 
17 int getf(int x)
18 {
19     return x = f[x] ? f[x] : f[x] = getf(f[x]);
20 }
21 
22 bool merge(int a, int b)
23 {
24     int t1 = getf(a);
25     int t2 = getf(b);
26     if(t1 != t2){
27         f[t2] = t1;
28         return true;
29     }
30     return false;
31 }
32 
33 void kruskal()
34 {
35     for(int i = 1; i <= M; ++i)
36         f[i] = i;
37     sort(e, e+N, Edge());
38     int cnt = 0;
39     int ans = 0;
40     bool success = false;
41     for(int i = 0; i < N; ++i){
42         if(merge(e[i].u, e[i].v)){
43             ans += e[i].w;
44             ++cnt;
45         }
46         if(cnt == M-1){
47             success = true;
48             break;
49         }
50     }
51     if(success)
52         printf("%d\n", ans);
53     else
54         printf("?\n");
55 }
56 
57 int main()
58 {
59     while(scanf("%d%d", &N, &M), N){
60         for(int i = 0; i < N; ++i){
61             scanf("%d%d%d", &e[i].u, &e[i].v, &e[i].w);
62         }
63         if(N < M-1) //明显统计数据不足
64             printf("?\n");
65         else
66             kruskal();
67     }
68     return 0;
69 }

 1 #include <cstdio>
 2 #include <cstring>
 3 
 4 const int INF = 0x3f3f3f3f;
 5 int N, M;
 6 int e[105][105];
 7 int dis[105];
 8 bool vis[105];
 9 
10 void prim()
11 {
12 
13     for(int i = 1; i <= M; ++i)
14         dis[i] = e[1][i];
15     vis[1] = true;
16     int ans = 0;
17     int cnt = 1;
18     bool success = true;
19     while(cnt<M){
20         int min_dis = INF, u;
21         for(int i = 1; i <= M; ++i){
22             if(!vis[i] && dis[i]<min_dis){
23                 min_dis = dis[u = i];
24             }
25         }
26         if(min_dis == INF){
27             success = false;
28             break;
29         }
30         vis[u] = true;
31         ++cnt;
32         ans += dis[u];
33         for(int i = 1; i <= M; ++i){
34             if(!vis[i] && e[u][i]<dis[i]){
35                 dis[i] = e[u][i];
36             }
37         }
38     }
39     if(success)
40         printf("%d\n", ans);
41     else
42         printf("?\n");
43 }
44 
45 int main()
46 {
47     while(scanf("%d%d", &N, &M), N){
48         memset(vis, 0, sizeof(vis));
49         for(int i = 1; i <= M; ++i)
50             for(int j = 1; j <= M; ++j)
51                 e[i][j] = (i == j ? 0 : INF);
52         int u, v, w;
53         for(int i = 1; i <= N; ++i){
54             scanf("%d%d%d", &u, &v, &w);
55             e[u][v] = e[v][u] = w;
56         }
57         if(N < M-1)
58             printf("?\n");
59         else
60             prim();
61     }
62     return 0;
63 }