hdu1863（最小生成树）

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<vector>
#include<algorithm>
#include<stack>
#include<queue>
using namespace std;
#define INF 1000000000
#define eps 1e-8
#define pii pair<int,int>
#define LL long long int
int n,m,p[105],num;
LL ans;
struct node
{
    int u,v;
    LL w;
} e[10010];
bool cmp(node aa,node bb)
{
    return aa.w<bb.w;
}
int finds(int x)
{
    return p[x]==x?x:p[x]=finds(p[x]);
}
int main()
{
   // freopen("in1.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    while(scanf("%d%d",&n,&m)==2)
    {
        if(n==0) break;
        ans=0;
        num=0;
        for(int i=0; i<n; i++)
        {
            scanf("%d%d%I64d",&e[i].u,&e[i].v,&e[i].w);
        }
        for(int i=1; i<=m; i++)
        {
            p[i]=i;
        }
        sort(e,e+n,cmp);
        for(int i=0; i<n; i++)
        {
            int x=finds(e[i].u);
            int y=finds(e[i].v);
            if(x!=y)
            {
                ans+=e[i].w;
                num++;
                p[x]=y;
            }
        }
        if(num==m-1)
            printf("%I64d\n",ans);
        else
            printf("?\n");
    }
    //fclose(stdin);
    //fclose(stdout);
    return 0;
}