HDU1863畅通工程---并查集+最小生成树

#include<cstdio>
#include<algorithm>
#define MAX 105

struct edge
{
    int from,to;
    long long cost;
}lm[MAX*MAX];

int N,M,father[MAX],i;

bool cmp(edge a,edge b)
{
    return a.cost<b.cost;
}

void init()
{
    for(int i=1;i<=N;i++)
        father[i]=i;
}

int Find(int x)
{
    if(x==father[x])return x;
    return father[x]=Find(father[x]);
}

bool Same(int x,int y)
{
    return Find(x)==Find(y);
}

void unionset(int x,int y)
{
    int u=Find(x),v=Find(y);
    if(u==v)return;
    father[u]=v;
}

long long kruskal()
{
    long long res=0;
    std::sort(lm+1,lm+1+M,cmp);
    for(i=1;i<=M;i++)
    {
        if(Same(lm[i].from,lm[i].to))continue;
        unionset(lm[i].from,lm[i].to);
        res+=lm[i].cost;
    }
    return res;
}

int main()
{
    while(scanf("%d%d",&M,&N)==2)
    {
        if(!M)break;
        init();
        for(i=1;i<=M;i++)
        {
            scanf("%d%d%lld",&lm[i].from,&lm[i].to,&lm[i].cost);
        }
        long long res=kruskal();
        for(i=1;i<=N;i++)
            if(!Same(i,1))
                res=-1;
        if(res==-1)
            printf("?
");
        else
            printf("%lld
",res);
    }
    return 0;
}