acwing .361.观光的奶牛

 

 

#include<bits/stdc++.h>
#define N 10010
using namespace std;
int head[N],to[N],vis[N],net[N],cut;
int num[N],f[N];
int vv[N];
queue<int>dl;
double dis[N];
int l,p;
void add(int from,int t,int v)
{
    net[++cut]=head[from];
    to[cut]=t;
    vis[cut]=v;
    head[from]=cut;
}
int spfa(double mid)//数据类型要一致
{
    for(int i=1;i<=l;i++)
        dl.push(i),f[i]=1,dis[i]=num[i]=0;
    while(dl.size())
    {
        int x=dl.front();
        dl.pop();
        f[x]=0;    
        for(int i=head[x];i;i=net[i])
        {
            int y=to[i];
            double v=vis[i]*mid-vv[x];
            if(dis[x]+v<dis[y])
            {
                dis[y]=dis[x]+v;
                num[y]=num[x]+1;
                if(num[y]>=p)return 1;
                if(!f[y])
                {
                    dl.push(y);
                    f[y]=1;
                }
            }
        }
    }
    return 0;
}
int main()
{
    scanf("%d%d",&l,&p);
    for(int i=1;i<=l;i++)
        scanf("%d",&vv[i]);
    for(int i=1;i<=p;i++)
    {
        int x,y,z;
        scanf("%d%d%d",&x,&y,&z);
        add(x,y,z);
    }
    double l=0,r=1e8;
    while(r-l>0.0001)
    {
        double mid=(l+r)/2;
        if(spfa(mid))l=mid;
            else r=mid;
    }
    printf("%.2lf",r);
    return 0;
}