又是被黄题卡住的一天...

在强连通的诱惑下我毅然决然选择来讨论板白嫖求助，希望能有dalao发现

代码奉上

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;
#define N 23333
#define inf 0x7fffffff
int t,n,m,num,head[N],dis[N],visn[N]; 
bool vis[N],jud;
struct Edge{
	int to;
	int next;
	int val;
}edge[N];
void Addedge(int u,int v,int w)
{
	edge[++num].to=v;
	edge[num].next=head[u];
	edge[num].val=w;
	head[u]=num;
}
int main()
{
	ios::sync_with_stdio(false);
	cin>>t;
	while(t--)
	{
		memset(head,0,sizeof(head));
		memset(edge,0,sizeof(edge));
		memset(vis,false,sizeof(vis));
		memset(visn,0,sizeof(visn));
		queue<int>q;
		jud=false;
		cin>>n>>m;
		for(register int i=1;i<=n;i++)dis[i]=inf;
		for(register int i=1;i<=m;i++)
		{
			int x,y,z;
			cin>>x>>y>>z;
			Addedge(x,y,z);
			if(z>=0)Addedge(y,x,z);
		}
		dis[1]=0;q.push(1);vis[1]=true;visn[1]++;
		while(!q.empty())
		{
			int fro=q.front();q.pop();vis[fro]=false;
			for(register int i=head[fro];i;i=edge[i].next)
			{
				int to=edge[i].to;
				if(dis[to]>dis[fro]+edge[i].val)
				{
					dis[to]=dis[fro]+edge[i].val;
					visn[to]++;
					if(visn[to]>=n){jud=true;break;}
					if(!vis[to]){q.push(to);vis[to]=true;}
				}
			}
			if(jud)break;
		}
		jud?cout<<"YES\n":cout<<"NO\n";
	}
	return 0;
 } 

太蒻了写SPFA果然容易炸（doogle