poj3164

朱刘算法
差分？。。。(粘的别人代码)
考虑存在环，则该环中必定去一条边，且往外扩展一条边，那先假设环上所有边都选，则实际选择+w[v出]-w[v环上入]

#include<cstdio>
#include<cmath>
using namespace std;
const int inf=0x7fffffff;
int n,m,cnt_edge,pre[105],color[105],mark[105];
struct point{int x,y;}P[105];
struct Edge{int u,v;double w;}edge[10005];
double in[105];
void AddEdge(int u,int v,double w){edge[cnt_edge].u=u,edge[cnt_edge].v=v,edge[cnt_edge].w=w,cnt_edge++;}
inline double Cal(int x1, int y1,int x2, int y2){return sqrt(1.0*(x1-x2)*(x1-x2)+1.0*(y1-y2)*(y1-y2));}
double zhuliu(int root,int n,int m){
    int i,j,u,v,cnt=0;double w,res=0;
    while(1){
        for(i=1;i<=n;i++)in[i]=inf;
        for(i=0;i<m;i++){
            u=edge[i].u,v=edge[i].v,w=edge[i].w;
            if(in[v]>w&&u!=v)in[v]=w,pre[v]=u;
        }
        for(i=1;i<=n;i++)if(i!=root && in[i]==inf)return -1;
        for(i=1;i<=n;i++)color[i]=mark[i]=0;
        mark[root]=1,in[root]=cnt=0;
        for(i=1;i<=n;i++){
            res+=in[i],v=i;
            while(mark[v]!=i&&color[v]==0&&v!=root)mark[v]=i,v=pre[v];
            if(v!=root&&color[v]==0){
                cnt++;
                for(u=pre[v];u!=v;u=pre[u])color[u]=cnt;
                color[v]=cnt;
            }
        }
        if(cnt==0)break;
        for(i=1;i<=n;i++)if(color[i]==0)color[i]=++cnt;
        for(i=0;i<m;i++){
            v=edge[i].v;
            edge[i].u=color[edge[i].u],edge[i].v=color[edge[i].v];
            if(edge[i].u!=edge[i].v)edge[i].w-=in[v];
        }
        n=cnt,root=color[root];
    }
    return res;
}
 
int main(){
    while(scanf("%d%d",&n,&m)!=EOF){
        int i,j,f,t;
        cnt_edge=0;
        for(i=1;i<=n;i++)scanf("%d%d",&P[i].x,&P[i].y);
        for(i=0;i<m;i++){
            scanf("%d%d",&f,&t);
            if(f!=t)AddEdge(f,t,Cal(P[f].x,P[f].y,P[t].x,P[t].y));
        }
        double ans=zhuliu(1,n,cnt_edge);
        if(ans!=-1)printf("%.2f
",ans);else puts("poor snoopy");
    }
    return 0;
}