1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cstdlib>
 5 #include <cmath>
 6 #include <cctype>
 7 #include <algorithm>
 8 using namespace std;
 9
10 const int MAXN = 2e3+ 3;
11 int pre[MAXN];
12 int m,n;
13
14 int Find(int x)  //并查集
15 {
16     return x == pre[x] ? x :(pre[x] = Find(pre[x]));
17 }
18
19 struct Node //存图
20 {
21     int u, v, w;
22 }cy[103];
23
24 int mycmp(Node a,Node b)
25 {
26     return a.w < b.w;
27 }
28
29 void mst()
30 {
31     for(int i = 0 ; i < 102; i++)
32         pre[i] = i;
33 }
34
35 int kru()//算法的具体实现
36 {
37     int ans = 0;
38     int cnt = 0;
39     for(int i = 1; i <= n; i++)
40     {
41         int fv = Find(cy[i].v);
42         int fu = Find(cy[i].u);
43         if(fv != fu)
44         {
45             pre[fv] = fu;
46             ans += cy[i].w;
47             cnt ++;
48         }
49         if(cnt == m -1)
50         {
51             return ans;
52             break;
53         }
54     }
55     return -1;
56 }
57
58 int main()
59 {
60     //freopen("in.cpp","r",stdin);
61     while(~scanf("%d%d",&n,&m) && n)
62     {
63         mst();
64         for(int i = 1; i <= n; i++)
65             scanf("%d%d%d",&cy[i].u, &cy[i].v, &cy[i].w);
66         sort(cy + 1, cy + n + 1, mycmp);
67         int ans = kru();
68         if(ans != -1)
69             printf("%d\n",ans);
70         else
71             printf("?\n");
72     }
73     return 0;
74 }

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cstdlib>
 5 #include <cmath>
 6 #include <cctype>
 7 #include <algorithm>
 8 using namespace std;
 9
10 const int MAXN = 103;
11 const int INF = 0x3f3f3f3f;
12 int edge[MAXN][MAXN];   //用于存放图
13 int used[MAXN];//用于标记点是否已加入到最小生成树那个的集合中
14 int lowcost[MAXN];   //用于存放集合外的点到集合内的点的最短距离，每加入一个点需要更新一次
15 int N,M;
16
17 int prim(int start,int maxn)  //利用prim算法计算最小生成树
18 {
19    memset(used, 0, sizeof(used));
20    for(int i = 1; i <= maxn; i++)
21    {
22        lowcost[i] = edge[start][i];
23    }
24    used[start] = 1;
25    int sumweight = 0;
26    int ok = 0;
27    for(int i = 1; i <= maxn; i++)
28    {
29        int minn = INF ;
30        int v = -1;
31        for(int j = 1; j <= maxn; j++)
32        {
33            if(used[j] == 0 && lowcost[j] < minn)
34            {
35                minn = lowcost[j];
36                v = j;
37            }
38        }
39        //cout << v << " ";
40        if(v != -1)
41        {
42            ok++;
43            used[v] = 1;
44            sumweight += lowcost[v];
45            for(int j = 1; j <= maxn; j++)
46            {
47                if(used[j] == 0 && lowcost[j] > edge[v][j])
48                {
49                    lowcost[j] = edge[v][j];
50                }
51            }
52        }
53    }
54    if(ok == maxn -1)
55      return sumweight;
56    return -1;
57 }
58
59 int main()
60 {
61     while(cin >> N >> M && N)
62     {
63         memset(edge, 0x3f, sizeof(edge));
64         while(N--)
65         {
66             int u, v, w;
67             cin >> u >> v >> w;
68             edge[u][v] = edge[v][u] = w;
69         }
70         int ans = prim(1, M);
71         if(ans < 0) cout << "?" <<endl;
72         else cout << ans << endl;
73     }
74     return 0;
75 }

 1 import java.util.Scanner;
 2 import java.util.Comparator;
 3 import java.util.Arrays;
 4 import java.text.DecimalFormat;
 5
 6 class Vge{
 7     int u;
 8     int v;
 9     int w;
10 }
11
12 class mycmp implements  Comparator<Vge>{
13     public int compare( Vge A, Vge B ){
14             if( A.w - B.w != 0 )
15                 return A.w - B.w;
16             else
17                 return A.w - B.w;
18       }
19 }
20
21 public class Main{
22     final static int MAXN = 100 + 3;
23     static int[] pre = new int[ MAXN ];
24     static Vge[] clg = new Vge[ MAXN * MAXN ];
25     public static void main( String[] args ){
26         Scanner sc = new Scanner( System.in );
27         int n, m;
28         while( sc.hasNextInt() ){
29             n = sc.nextInt();
30             m = sc.nextInt();
31             if( n == 0 ) break;
32             for( int i = 0; i < n; i++ ){
33                 clg[ i ] = new Vge();
34                 clg[ i ].u = sc.nextInt();
35                 clg[ i ].v = sc.nextInt();
36                 clg[ i ].w = sc.nextInt();
37             }
38             mst( m );
39             int ans = ksu( n, m );
40             if( ans == -1 ) System.out.println( "?" );
41             else System.out.println( ans );
42         }
43         sc.close();
44     }
45     public static void mst( int n ){
46         for( int i = 0; i <= n; i++ ){
47             pre[i] = i;
48         }
49     }
50     public static int find( int x ){
51         return x == pre[ x ] ?   x :  ( pre[ x ] = find( pre[ x ] ) );
52     }
53     public static int ksu( int n, int m ){
54         Arrays.sort( clg, 0, n, new mycmp() );
55         int cnt = 0;
56         int ans = 0;
57         for( int i = 0; i < n; i++ ){
58             int fu = find( clg[ i ].u );
59             int fv = find( clg[ i ].v );
60             if( fu != fv ){
61                 ans += clg[i].w;
62                 cnt ++;
63                 pre [ fv ] = fu;
64             }
65             if( cnt == m - 1 ) return ans;
66         }
67         return -1;
68     }
69 }