题意:
有向图，求以1为根的最小树形图的边权之和。

解析:
练了下模板。
算法流程哪都有。

代码:

#include <cmath>
#include <vector>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define N 110
#define M 11000
#define x first
#define y second
#define eps 1e-6
#define INF 0x7fffffff
using namespace std;
typedef pair<double,double>Pa;
int tot;
struct Edge
{
    int u,v;
    double val;
    Edge(){}
    Edge(int _u,int _v,double _val):u(_u),v(_v),val(_val){}
}edge[M];
Pa point[N];
int n,m,u,v;
double get_dis(Pa &a,Pa &b)
{
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
namespace Minimal_Tree_Graph
{
    #define fr edge[i].u
    #define to edge[i].v
    #define Val edge[i].val
    int id[N],pre[N],vis[N];
    double in[N];
    double work(int root,int n)
    {
        double ret=0;
        while(true)
        {
            for(int i=1;i<=n;i++)
                in[i]=INF;
            for(int i=1;i<=m;i++)
                if(in[to]>Val&&fr!=to)
                    in[to]=Val,pre[to]=fr;
            for(int i=1;i<=n;i++)
                if(in[i]==INF&&i!=root)return -1;
            int cnt_ring=0;
            memset(id,-1,sizeof(id));
            memset(vis,-1,sizeof(vis));
            in[root]=0;
            for(int i=1;i<=n;i++)
            {
                ret+=in[i];
                int v=i;
                while(vis[v]!=i&&id[v]==-1&&v!=root){vis[v]=i;v=pre[v];}
                if(v!=root&&id[v]==-1)
                {
                    cnt_ring++;
                    for(int u=pre[v];u!=v;u=pre[u])id[u]=cnt_ring;
                    id[v]=cnt_ring;
                }
            }
            if(!cnt_ring)break;
            for(int i=1;i<=n;i++)
                if(id[i]==-1)id[i]=++cnt_ring;
            for(int i=1;i<=m;i++)
            {
                int u=edge[i].u;
                int v=edge[i].v;
                edge[i].u=id[u];
                edge[i].v=id[v];
                if(id[u]!=id[v])edge[i].val-=in[v];
            }
            n=cnt_ring;
            root=id[root];
        }
        return ret;
    }
}
int main()
{
    while(~scanf("%d%d",&n,&m))
    {
        for(int i=1;i<=n;i++)
            scanf("%lf%lf",&point[i].x,&point[i].y);
        for(int i=1;i<=m;i++)
        {
            scanf("%d%d",&u,&v);
            double val=get_dis(point[u],point[v]);
            if(u==v)edge[i]=Edge(u,v,INF);
            else edge[i]=Edge(u,v,val);
        }
        double ans=Minimal_Tree_Graph::work(1,n);
        if(ans==-1)puts("poor snoopy");
        else printf("%.2f\n",ans);
    }
}