求解，下面是我的代码

// luogu-judger-enable-o2
#ifndef _SPFA
#define _SPFA 2018.6.11

# include <cstdio>
# include <iostream>
# include <queue>
# include <cstring>
# define _cin std::ios::sync_with_stdio(0)
# define INF 0x7fffffff
# define rg register int
# define il inline
# define N 1000000
using namespace std;
struct edge
{
    int next;
    int to;
    int w;
}e[(N+1)<<1];
int head[N+1];
int book[N+1];
int dis[N+1];
int edge_sum=0;
int n,m;
template <class T> il bool SPFA(T s);
template <class A> il void add_edge(A &u,A &,A &w);
int main()
{
    _cin;
    cin.tie(); 
    rg t;
    cin>>t;
    while(t--)
    { 
        edge_sum=0;
        rg u,v,w;
        memset(head,0,sizeof(head));
        memset(dis,0x7f,sizeof(dis));
    	memset(book,0,sizeof(book));
    	cin>>n>>m;
    	for(rg i = 1;i<=m;i++)
    	{
            edge_sum++;
            cin>>u>>v>>w;
    		e[edge_sum].next=head[u];
    		e[edge_sum].to=v;
    		e[edge_sum].w=w;
    		head[u]=edge_sum;
    		
            if(w >= 0)
            {
                edge_sum++;
                e[edge_sum].next=head[v];
                e[edge_sum].to=u;
                e[edge_sum].w=w;
                head[v]=edge_sum;
            }
        } 
        if(SPFA(1)) cout<<"YE5"<<endl;
        else cout<<"N0"<<endl;
    }
    return 0;
}
template <class A> il void add_edge(A &u,A &v,A &w)
{
    edge_sum++;
    e[edge_sum].next=head[u];
    e[edge_sum].to=v;
    e[edge_sum].w=w;
    head[u]=edge_sum;
    return;
}
template <class T> il bool SPFA(T s)
{
    queue <int> a;
    dis[s]=0;
    a.push(s);
    book[s]=1;
    while(a.size()>0)
    {
        int k=a.front();
        a.pop();
        book[k]=0;
        for(int i = head[k];i;i=e[i].next)
        {
            if(dis[k] < INF and dis[e[i].to]>dis[k]+e[i].w)
                {
                    dis[e[i].to]=dis[k]+e[i].w;
                    if(e[i].to == s) return true;
                    if(!book[e[i].to])
                        {
                            a.push(e[i].to);
                            book[e[i].to]=1;
                        }
                }
        }
    }
    return false;
}

#endif