Bellman-Floyd 负环模板

#include <cstdio>
#include <iostream>
#include <vector>
#include <cstring>
#define inf 0x3f3f3f3f
using namespace std ;
typedef long long ll ;
const int N = 2e3 + 8  ;
int n, m ;
//int u[N], v[N], w[N] ;
int dis[N] ;
bool vis[N] ;

void init() {
	for (int i = 1 ; i <= n ; i ++)
		dis[i] = inf ;
}
vector<int>u, v, w ;

int main() {
	std::ios::sync_with_stdio(false) ;
	std::cin.tie(0) ;
	int T ;
	cin >> T ;
	while (T --) {
		cin >> n >> m ;
		init();
		dis[1] = 0 ;
		for (int i = 0 ; i < m ; i ++) {
			int x, y, z ;
			cin >> x >> y >> z ;
			u.push_back(x), v.push_back(y), w.push_back(z) ;
//			u.push_back(y), v.push_back(x), w.push_back(z) ;
		}
		for (int i = 1 ; i <= n - 1 ; i ++)  {
			for (int j = 0 ; j < u.size()  ; j ++) {
				if (dis[v[j]] > dis[u[j]] + w[j])
					dis[v[j]] = dis[u[j]] + w[j] ;
			}
		}
		int flag  = 0 ;
		for (int i = 0 ; i < u.size()  ; i ++) {
			if (dis[v[i]] > dis[u[i]] + w[i]) {
				flag  = 1 ;
				break ;
			}
		}
		if (flag == 1 )
			cout << "YES" << '\n' ;
		else
			cout << "NO" << '\n' ;

	}
	return 0 ;
}