poj3164 最小树形图板子题

/*

思路很简单，也不知道哪里错了TAT

*/

/*
N个点通过笛卡尔坐标表示
根节点是1，求最小树形图 
*/
#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#define MAXN 105
#define INF 0x3f3f3f3f
using namespace std;
struct Edge{
     int u,v;
     double cost;
     Edge(int uu=0,int vv=0,double cc=0.0):u(uu),v(vv),cost(cc){}
}edge[MAXN*MAXN];
struct node{
     int x,y;
}nodes[MAXN];
double dist(int u,int v){
     return sqrt((double)(nodes[u].x-nodes[v].x)*(nodes[u].x-nodes[v].x)+
                  (nodes[u].y-nodes[v].y)*(nodes[u].y-nodes[v].y));
} 
int pre[MAXN],id[MAXN],vis[MAXN];
double in[MAXN];
double zhuliu(int root, int nv, int ne)
{
    double ans = 0;
    int u, v, i, cnt;
    while(true){
        //0.初始化
        for(i = 1; i <= nv; ++i) in[i] = INF;
        //1.找最小入边集
        for(i = 1; i <= ne; ++i){
            u = edge[i].u; v = edge[i].v;
            if(edge[i].cost < in[v] && u != v){
                in[v] = edge[i].cost; pre[v] = u;
            }
        }
        for(i = 1; i <= nv; ++i)
            if(in[i]==INF && i!=root)
                return -1;
        //2.找非根无入边点(略)，因为必定有解
        //3.找环，加权，重新标号
        memset(id, -1, sizeof(id));
        memset(vis, -1, sizeof(vis));
        cnt = in[root] = 0;
        for(i = 1; i <= nv; ++i){
            ans += in[i]; v = i;
            while(vis[v] != i && v != root && id[v] == -1){
                vis[v] = i; v = pre[v];
            }
            if(v != root && id[v] == -1){
                for(u = pre[v]; u != v; u = pre[u])
                    id[u] = cnt;
                id[v] = cnt++;
            }
        }
        if(cnt == 0) break; //无环，算法完成
        for(i = 1; i <= nv; ++i) 
            if(id[i] == -1) id[i] = cnt++;
        //4.缩点，遍历每一条边，重新构图
        for(i = 1; i <= ne; ++i){
            v = edge[i].v;
            edge[i].u = id[edge[i].u];
            edge[i].v = id[edge[i].v];
            if(edge[i].u != edge[i].v) edge[i].cost -= in[v];
        }
        //顶点数减少
        nv = cnt; root = id[root];
    }
    return ans;
}
int main(){
     int n,m,u,v;
     while(scanf("%d%d",&n,&m)==2){
         for(int i=1;i<=n;i++)
             scanf("%d%d",&nodes[i].x,&nodes[i].y);
         int totm=0;
        for(int i=1;i<=m;i++){
             scanf("%d%d",&u,&v);
             if(u!=v)
                 edge[++totm]=Edge(u,v,dist(u,v));
         }
         int root=1;
         double res=zhuliu(root,n,totm);
         if(res==-1)
             puts("poor snoopy");
         else 
             printf("%.2lf
",res);
     }
     return 0;
}