spfa 90分求助

#include<cstdio>
#include<iostream>
#include<queue>
#include<cstring>
using namespace std;
int n,m,T,flag;
struct node
{
	int from;
	int to;
	int next;
	int data;
}ed[100086<<1];
int v[100086<<1],tot;
void add(int x,int y,int zhi)
{
	ed[++tot].from=x;
	ed[tot].to=y;
	ed[tot].data=zhi;
	ed[tot].next=v[x];
	v[x]=tot;
}
queue<int>q;
int dis[100086],vis[100086],f[100086];
void spfa()
{
	vis[1]=0;
	q.push(1);
	for(int i=1;i<=n;i++)
		dis[i]=1e9;
	f[1]++;
	dis[1]=0;
	while(!q.empty())
	{
		int w=q.front();
		q.pop();
		vis[w]=0;
		for(int i=v[w];i;i=ed[i].next)
		{
			int t=ed[i].to;
			if(dis[t]>dis[w]+ed[i].data)
			{
				dis[t]=dis[w]+ed[i].data;
				if(vis[t]==0)
				{
					vis[t]=1;
					q.push(t);
					f[t]++;
				}
				if(f[t]>20)
				{
					flag=1;
					return;
				}
			}
			
		}
	}
}
void clean()
{
	flag=0;
	memset(vis,0,sizeof(vis));
	memset(f,0,sizeof(f));
	memset(ed,0,sizeof(ed));
	memset(v,0,sizeof(v));
}
int a,b,c;
int main()
{
	freopen("testdata.in","r",stdin);
	freopen("b.out","w",stdout);
	scanf("%d",&T);
	while(T>0)
	{
		clean();
		--T;
		scanf("%d%d",&n,&m);
		for(int i=1;i<=m;i++)
		{
			scanf("%d%d%d",&a,&b,&c);
			if(c>=0)
				add(b,a,c);
			add(a,b,c);
		}
		spfa();
		if(flag==0)
		{
			printf("N0");
			printf("\n");
		}
		else
		{
			printf("YE5");
			printf("\n");
		}
	}
	fclose(stdin);
	fclose(stdout);
	return 0;
}