WA 求调

#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int N=2e3+5;
struct STU{
	ll u,w;
}now;
ll dist[N],cnt[N];
bool p[N];
int main(){
	int T,n,m;
	scanf("%d",&T);
	while(T--){
		vector<STU>v[2005];
		scanf("%d%d",&n,&m);
		for(int i=1;i<=m;i++){
			int a,b,c;
			scanf("%d%d%d",&a,&b,&c);
			now.u=b,now.w=c;
			v[a].push_back(now);
			if(c>=0){
				now.u=a;
				v[b].push_back(now);
			}
		}
		memset(dist,0x3f,sizeof(dist));
		memset(cnt,0,sizeof(cnt));
		memset(p,0,sizeof(p));
		queue<int>q;
		q.push(1);
		p[1]=1,dist[1]=0;
		bool ok=0;
		while(!q.empty()){
			if(ok)break;
			int t=q.front();
			p[t]=0;
			q.pop();
			for(int i=0;i<v[t].size();i++){
				int a=v[t][i].u,b=v[t][i].w;
				if(dist[t]+b<dist[a]){
					dist[a]=dist[t]+b;
					if(!p[i]){
						if(++cnt[a]>=n){
							printf("YES\n");
							ok=1;
							break;
						}
						p[a]=1;
						q.push(a);
					}
				}
			}
		}
		if(!ok)printf("NO\n");
	}
	return 0;
}