HDU 3371 Connect the Cities

题解：最小生成树

#include <cstdio>
#include <algorithm>
using namespace std;
struct node{int a,b,l;}seg[25005];
int T,z,x,t,f[505],m,n,k; char c;
int sf(int x){return f[x]==x?x:f[x]=sf(f[x]);}
bool cmp(node a,node b){return a.l<b.l;}
void scan(int &x){
    while(c=getchar(),c<'0'||c>'9');x=c-'0';
    while(c=getchar(),c>='0'&&c<='9')x=x*10+c-'0';
}
int main(){
    scan(T);
    while(T--){
        scan(n),scan(m),scan(k);
        int ans=0;
        for(int i=1;i<=n;i++)f[i]=i;
        int cnt=n-1;
        for(int i=0;i<m;i++)scan(seg[i].a),scan(seg[i].b),scan(seg[i].l);
        while(k--){
            scan(t);scan(x);
            int q=sf(x);
            for(int i=1;i<t;i++){
                scan(z);
                int w=sf(z);
                if(q!=w)f[w]=q,cnt--;
            }
        }sort(seg,seg+m,cmp);
        for(int i=0;i<m&&cnt;i++){
            int q=sf(seg[i].a),w=sf(seg[i].b);
            if(q!=w)cnt--,f[q]=w,ans+=seg[i].l;
        }
        if(cnt)puts("-1");else printf("%d\n",ans);
    }
    return 0;
}