HDU - 1863

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int maxn=1000+10;
const int maxm=1000+10;

struct Edge
{
    int u,v,dist;
    Edge(){}
    Edge(int u,int v,int d):u(u),v(v),dist(d){}
    bool operator<(const Edge &rhs)const
    {
        return dist<rhs.dist;
    }
};

struct Kruskal
{
    int n,m;
    Edge edges[maxm];
    int fa[maxn];
    int findset(int x){ return fa[x]==-1?x: fa[x]=findset(fa[x]); }

    void init(int n)
    {
        this->n=n;
        m=0;
        memset(fa,-1,sizeof(fa));
    }

    void AddEdge(int u,int v,int dist)
    {
        edges[m++]=Edge(u,v,dist);
    }

    int kruskal()
    {
        int sum=0,cnt=0;
        sort(edges,edges+m);

        for(int i=0;i<m;i++)
        {
            int u=edges[i].u, v=edges[i].v;
            if(findset(u)  != findset(v))
            {
                sum +=edges[i].dist;
                fa[findset(u)] = findset(v);
                if(++cnt>=n-1) return sum;
            }
        }
        return -1;
    }
}KK;

int main()
{
    int n,m;
    while(scanf("%d",&m)==1&&m)
    {
        scanf("%d",&n);
        KK.init(n);
        while(m--)
        {
            int u,v,d;
            scanf("%d%d%d",&u,&v,&d);
            KK.AddEdge(u,v,d);
        }
        int ans = KK.kruskal();
        if(ans==-1) printf("?\n");
        else printf("%d\n",ans);
    }
    return 0;
}