题解：

分数规划+判断负环。

代码：

#include <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define N 1010
#define M 5050
#define eps 1e-8
using namespace std;
double mid,fun[N];
struct Eli
{
    int v,n;
    double f,l;
    void re(){l=mid*f-fun[v];}
}e[M];
int head[N],cnt;
inline void add(int u,int v,double l)
{
    e[++cnt].v=v;
    e[cnt].f=l;
    e[cnt].n=head[u];
    head[u]=cnt;
}
int n,m,num[N];
double dist[N];
queue<int>q;
bool in[N];
bool spfa()
{
    memset(in,0,sizeof in);
    memset(num,0,sizeof num);
    memset(dist,0x43,sizeof dist);
    while(!q.empty())q.pop();
    int i,u,v;
    q.push(1),dist[1]=0,num[1]=1;
    while(!q.empty())
    {
        u=q.front(),q.pop(),in[u]=0;
        for(i=head[u];i;i=e[i].n)
        {
            v=e[i].v;
            if(dist[v]>dist[u]+e[i].l+eps)
            {
                if(++num[v]>n)return 1;
                dist[v]=dist[u]+e[i].l;
                if(!in[v])in[v]=1,q.push(v);
            }
        }
    }
    return 0;
}
bool check()
{
    for(int i=1;i<=cnt;i++)e[i].re();
    return spfa();
}
int main()
{
    int i,a,b;
    double c;

    scanf("%d%d",&n,&m);
    for(i=1;i<=n;i++)scanf("%lf",&fun[i]);
    for(i=1;i<=m;i++)
    {
        scanf("%d%d%lf",&a,&b,&c);
        add(a,b,c);
    }
    double l=0,r=1e6;
    for(i=60;i--;)
    {
        mid=(l+r)/2.0;
        if(check())l=mid;
        else r=mid;
    }
    printf("%.2lf\n",l);
    return 0;
}