1072 Gas Station （30 分）（最短路径）

 

#include<bits/stdc++.h>

using namespace std;
const int N=1e3+100;
int n,m,k,Ds;
int mp[N][N];
int dis[N];
int vis[N];
int inf=0x3f3f3f3f;
int toint(char s[])
{
    int sum=0;
    int len=strlen(s);
    for(int i=0;i<len;i++){
        if(s[i]=='G') continue;
        sum=sum*10+s[i]-'0';
    }
    if(s[0]=='G') return sum+n;
    return sum;
}

void Dijkstra(int v)
{
    fill(vis,vis+N,false);
    fill(dis,dis+N,inf);
    for(int i=1;i<=n+m;i++){
        dis[i]=mp[v][i];
    }
    dis[v]=0;
    for(int i=0;i<n+m;i++){
        int u=-1;
        int minn=inf;
        for(int j=1;j<=n+m;j++){
            if(!vis[j]&&minn>dis[j]){
                u=j;
                minn=dis[j];
            }
        }
        vis[u]=true;
        for(int j=1;j<=n+m;j++){
            if(!vis[j]&&dis[j]>mp[u][j]+dis[u]){
                dis[j]=mp[u][j]+dis[u];
            }
        }
    }
}
int main()
{
    scanf("%d %d %d %d",&n,&m,&k,&Ds);
    fill(mp[0],mp[0]+N*N,inf);
    for(int i=0;i<k;i++){
        char s1[5],s2[5];
        int num;
        scanf("%s %s %d",s1,s2,&num);
        int a=toint(s1);
        int b=toint(s2);
        mp[a][b]=mp[b][a]=num;
    }
    int id=-1;
    double maxDis=-1;
    double minAvg=inf;
    for(int i=n+1;i<=n+m;i++){
        Dijkstra(i);
        double avg=0;
        double Min=inf;
        bool flag=false;
        for(int j=1;j<=n;j++){
            if(dis[j]>Ds){
                flag=true;
                break;
            }
            if(Min>dis[j]){
                Min=dis[j];
            }
            avg+=1.0*dis[j]/n;
        }
        if(flag) continue;
        if(maxDis<Min){
            maxDis=Min;
            id=i;
            minAvg=avg;
        }
        else if(maxDis==Min&&minAvg>avg){
            id=i;
            minAvg=avg;
        }

    }
    if(id==-1) printf("No Solution\n");
    else{
        printf("G%d\n",id-n);
        printf("%.1f %.1f\n",maxDis,minAvg);
    }
    return 0;
}