瑾时后人

#include <bits/stdc++.h>
using namespace std;

int T;

struct edge {
	int from;
	int to;
	int w;
};

int main() {
	cin >> T;
	while (T--) {
		int n, m;
		cin >> n >> m;
		vector<edge> e;
		int d[4001];
		memset(d, 0x7f, sizeof (d));
		d[1] = 0;
		for (int i = 1; i <= m; i++) {
			int u, v, w;
			cin >> u >> v >> w;
			if (w >= 0) {
				e.push_back({u, v, w});
				e.push_back({v, u, w});
			} else {
				e.push_back({u, v, w});
			}
		}
		for (int i = 1; i < n; i++) {
			for (int j = 0; j < e.size(); j++) {//  此处不是j < m
				if (d[e[j].from] != 0x7f7f7f7f) {
					d[e[j].to] = min(d[e[j].to], d[e[j].from] + e[j].w);
				}
			}
		}
		bool flag = true;
		for (int j = 0; j < e.size(); j++) {//  此处同理
			if (d[e[j].from] != 0x7f7f7f7f && d[e[j].to] > d[e[j].from] + e[j].w) {
				flag = false;
				break;
			}
		}
		if (flag) {
			cout << "NO\n";
		} else {
			cout << "YES\n";
		}
	}
	return 0;
}