不输出答案为YES的情况， $A$ 了2个，$T$ 8个

#include<bits/stdc++.h>
#define me memset
#define int long long
using namespace std;
const int N=20010;
int n,m,cnt,dis[N],vis[N],head[N],sum[N],nx[N],to[N],val[N],T,f;
void add(int u,int v,int w){
	nx[++cnt]=head[u];
	to[cnt]=v;
	val[cnt]=w;
	head[u]=cnt;
}
signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);
	cin>>T;
	while(T--){
		cnt=f=0;
		me(dis,0,sizeof(dis));
		me(vis,0,sizeof(vis));
		me(sum,0,sizeof(sum));
		me(head,0,sizeof(head));
		me(nx,0,sizeof(nx));
		me(to,0,sizeof(to));
		me(val,0,sizeof(val));
		cin>>n>>m;
		for(int i=1;i<=m;i++){
			int u,v,w;
			cin>>u>>v>>w;
			add(u,v,w);
			if(w>=0){
				add(v,u,w);
			}
		}
		queue<int> q;
		for(int i=2;i<=n;i++){
			dis[i]=INT_MAX;
		}
		vis[1]=1;
		sum[1]=1;
		q.push(1);
		while(!q.empty()){
			int u=q.front();
			q.pop();
			vis[u]=0;
			for(int i=head[u];i;i=nx[i]){
				if(dis[to[i]]>dis[u]+val[i]){
					dis[to[i]]=dis[u]+val[i];
					if(vis[to[i]]==0){
						vis[to[i]]=1;
						q.push(to[i]);
						sum[to[i]]++;
						if(sum[to[i]]>n){
							f=1;
						}
					}
				}
			}
		}
		if(f==1){
			cout<<"YES"<<endl;
		}
		else{
			cout<<"NO"<<endl;
		}
	}
	return 0;
}