负环这道题大家都知道。 但如果用拓扑排序做这道题只能拿20分，其他的都是WA 蒟蒻的小代码,也有可能纯粹是本蒟蒻的码力不行：

#include <iostream>
#include <vector>
#include <queue>
using namespace std;

const int MAXN = 2005;
int n, m;
vector<pair<int, int>> edges[MAXN];
int inDegree[MAXN];
bool negativeCycle;

void topologicalSort() {
    queue<int> q;
    for (int i = 1; i <= n; i++) {
        if (inDegree[i] == 0) {
            q.push(i);
        }
    }

    while (!q.empty()) {
        int u = q.front();
        q.pop();

        for (auto edge : edges[u]) {
            int v = edge.first;
            int w = edge.second;
            inDegree[v]--;
            if (inDegree[v] == 0) {
                q.push(v);
            }
        }
    }
}

int main() {
    int T;
    cin >> T;
    while (T--) {
        cin >> n >> m;
        for (int i = 1; i <= n; i++) {
            edges[i].clear();
            inDegree[i] = 0;
        }
        negativeCycle = false;

        for (int i = 0; i < m; i++) {
            int u, v, w;
            cin >> u >> v >> w;
            edges[u].push_back({v, w});
            inDegree[v]++;
        }

        topologicalSort();

        for (int i = 1; i <= n; i++) {
            for (auto edge : edges[i]) {
                int v = edge.first;
                int w = edge.second;
                if (w < 0) {
                    negativeCycle = true;
                    break;
                }
            }
            if (negativeCycle) {
                break;
            }
        }

        if (negativeCycle) {
            cout << "YES" << endl;
        } else {
            cout << "NO" << endl;
        }
    }
    return 0;
}