HDU 4081 Qin Shi Huang's National Road System 最小生成树

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <stack>
#include <queue>
#include <cmath>
#include <vector>
using namespace std;
const int N=1005;
double x[N],y[N],d[N][N],a[N];
int fa[N],head[N],tot,cnt,T,n;
struct Edge{
    int v,next;
    double w;
}edge[N<<1];
void add(int u,int v,double w){ 
   edge[tot].v=v;
   edge[tot].w=w;
   edge[tot].next=head[u];
   head[u]=tot++;
}
struct Node{
  int u,v;
  bool mark;
  double w;
  bool operator<(const Node &rhs)const{
      return w<rhs.w;
  }
}p[N*N];
int find(int x){
    return x==fa[x]?x:fa[x]=find(fa[x]);
}
int s;
void dfs(int u,int f,double t){
   d[s][u]=t;
   for(int i=head[u];~i;i=edge[i].next){
        int v=edge[i].v;
        if(v==f)continue;
        dfs(v,u,max(t,edge[i].w));
   }
}
int main()
{
    scanf("%d",&T);
    while(T--){
        scanf("%d",&n);
        cnt=tot=0;
        memset(d,0,sizeof(d));
        for(int i=1;i<=n;++i){
            fa[i]=i,head[i]=-1;
            scanf("%lf%lf%lf",&x[i],&y[i],&a[i]);
            for(int j=1;j<i;++j){
              ++cnt;
              p[cnt].u=i,p[cnt].v=j;p[cnt].mark=0;
              p[cnt].w=sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]));
            }
        }
        sort(p+1,p+1+cnt);
        int tmp=n;
        double mst=0,ans=0;
        for(int i=1;i<=cnt;++i){
            int u=find(p[i].u),v=find(p[i].v);
            if(u!=v){
              --tmp;
              fa[u]=v;
              mst+=p[i].w;
              p[i].mark=1;
              add(p[i].u,p[i].v,p[i].w);
              add(p[i].v,p[i].u,p[i].w);
              if(tmp==1)break;
            }
        }
        for(int i=1;i<=n;++i){
            s=i;dfs(i,0,0);
        }
        for(int i=1;i<=cnt;++i){
           double aa=a[p[i].u]+a[p[i].v],bb;
           if(p[i].mark)bb=mst-p[i].w;
           else bb=mst-d[p[i].u][p[i].v];
           ans=max(ans,aa/bb);
        }
        printf("%.2f\n",ans);
    }
    return 0;
}