Coolest Ski Route-不定起点和终点----在有向变的情况下---求最长路

#include<bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const int MAX_V = 5006;
struct edge
{
    int to,cost;
};
typedef pair<int, int> P;
int V;
int n,m,st,ed;
int d[MAX_V];
vector<edge> G[MAX_V];
int ans;
void dijkstra(int s)
{
    priority_queue<P,vector<P>,greater<P> >que;
    for (int i=1;i<=n;i++){
        d[i]=INF;
    }
    d[s]=0;
    que.push(P(0,s));
    while(!que.empty())
    {
       // cout<<"---"<<endl;
        P p = que.top();
        que.pop();
        int v=p.second;
        if (d[v]<p.first)continue;
        for (int i=0; i<G[v].size(); i++)
        {
            edge e=G[v][i];
            if (d[e.to] > d[v]+e.cost)
            {
                d[e.to] = d[v]+e.cost;
                que.push(P(d[e.to],e.to));
            }
        }
    }
    for (int i=1;i<=n;i++){
        //cout<<d[i]<<endl;
        ans=min(ans,d[i]);
    }
   // cout<<ans<<endl;
}
int main()
{
    int book[5006];
    while(~scanf("%d%d",&n,&m)){
      int u,v,w;
       memset(book,0,sizeof(book));
       for (int i=1;i<=m;i++){
        scanf("%d%d%d",&u,&v,&w);
        book[v]=1;
        edge s;
        s.cost=-w;
        s.to=v;
        G[u].push_back(s);
       }
     for (int i=1;i<=n;i++){
       if (book[i]==0){
           dijkstra(i);
         }
       }
       printf("%d\n",-ans);
    }
    return 0;
}