CSES – High Score

#include<bits/stdc++.h>
#define int long long
#define pii pair<int,int>
#define f first
#define s second
#define fastio ios_base::sync_with_stdio(0);cin.tie(0)
using namespace std;
//declare
const int maxn = 2505;
int n,m,dis[maxn];
bool vis[maxn], reverse_vis[maxn];
vector<pii> G[maxn];
vector<int> reverse_G[maxn];
//
void bellman_ford(){
    for(int i=0;i<n-1;i++){
        for(int cur=1;cur<=n;cur++){
            for(auto [adj, w] : G[cur]){
                dis[adj] = min(dis[adj], dis[cur]+w);
            }
        }
    }
}
void dfs(int cur){
    if(vis[cur]) return;
    vis[cur] = 1;
    for(auto [adj,w] : G[cur]){
        dfs(adj);
    }
}
void reverse_dfs(int cur){
    if(reverse_vis[cur]) return;
    reverse_vis[cur] = 1;
    for(int adj : reverse_G[cur]){
        reverse_dfs(adj);
    }
}
signed main(){
    fastio;
    cin>>n>>m;
    for(int i=0;i<m;i++){
        int a,b,c; cin>>a>>b>>c;
        G[a].push_back({b,-c});
        reverse_G[b].push_back(a);
    }
    dis[1] = 0;
    for(int i=2;i<=n;i++) dis[i] = 1e18;
    bellman_ford();
    dfs(1); reverse_dfs(n);
    for(int cur=1;cur<=n;cur++){
        for(auto [adj, w] : G[cur]){
            if(dis[cur] + w < dis[adj]){
                if(vis[adj] && reverse_vis[adj]){
                    return cout<<-1<<"\n", 0;
                }
            }
        }
    }
    cout<<(-dis[n])<<"\n";
    return 0;
}