P1522 [USACO2.4] 牛的旅行 Cow Tours

//double <=1e30
#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cmath>
//#include<queue>
//#include<vector>
//#include<bits/stdc++.h>
#define ll long long
#define ddd printf("-----------------------\n");
using namespace std;
const int maxn=2e2+10 ;
const double inf=1e20;

char s[maxn];
int n,field[maxn],cnt;
double dis[maxn][maxn],lianc[maxn],zhijing[maxn],ans=inf;

struct node{
    int x,y;
    double dist(const node &p){
        return sqrt(1.0*((p.x-x)*(p.x-x)+(p.y-y)*(p.y-y)));
    }
}a[maxn];

void dfs(int id,int i)
{
    field[i]=id;
    for(int j=0;j<n;j++){
        if(dis[i][j]<inf&&field[j]==0){
            dfs(id,j);
        }
    }
}

int main()
{
    ios::sync_with_stdio(false);
    
    cin>>n;
    for(int i=0;i<n;i++)    cin>>a[i].x>>a[i].y;
    for(int i=0;i<n;i++){
        cin>>s;
        for(int j=0;j<n;j++){
            if(s[j]=='1'||i==j){
                dis[i][j]=a[i].dist(a[j]);
            }
            else dis[i][j]=inf;
        }
    }
    
    for(int i=0;i<n;i++) if(field[i]==0) dfs(++cnt,i);
    
    for(int k=0;k<n;k++)
        for(int i=0;i<n;i++)
            for(int j=0;j<n;j++)
                if(dis[i][j]>dis[i][k]+dis[k][j])
                    dis[i][j]=dis[i][k]+dis[k][j];
    
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
            if(dis[i][j]<inf)
                lianc[i]=max(lianc[i],dis[i][j]);
        zhijing[field[i]]=max(zhijing[field[i]],lianc[i]);
    }
    
    double tmp=0;
    for(int i=0;i<n;i++){
        for(int j=i+1;j<n;j++){
            if(field[i]!=field[j]){//dis[i][j]<inf&&    都相连了就一定在同一个连通块里面 
                tmp=max(max(zhijing[field[i]],zhijing[field[j]]),a[i].dist(a[j])+lianc[i]+lianc[j]);                 
                ans=min(tmp,ans);
            }
        }
    }
    printf("%.6lf\n",ans);
    return 0;
}