判负环

 

看 某个点的入队次数 times>=n

#include <bits/stdc++.h>
using namespace std ; 
 const int N=1e5+2,inf=0x7f7f3f;
 
 struct E{
 	int y,z;
 	E(int y0,int z0){
 		y=y0,z=z0;
	 }
	friend bool operator<(E x,E y){
		return x.z>y.z;
	}
 };
 vector<E> g[N];
 queue<int> q;
 int n,m,dis[N],b[N],tms[N];
 
 int spfa(int v0){
 	q.push(v0);
 	int i,x,y,z;
 	memset(dis,inf,sizeof(dis));
 	memset(b,0,sizeof(b)),memset(tms,0,sizeof(tms));
 	
 	dis[v0]=0,b[v0]=1;
	 tms[v0]++; 
 	
 	while(!q.empty()){
 		x=q.front(); q.pop();  
		 b[x]=0;
 		
 		for(i=0;i<g[x].size();i++){
 			y=g[x][i].y,z=g[x][i].z;
 			
 			if(dis[y]>dis[x]+z) {
 			   dis[y]=dis[x]+z;
				if(!b[y]){
					b[y]=1,q.push(y); tms[y]++;
					if(tms[y]>=n) return 0; 
				} 
			}
		 }
	 }
	 return 1;
 }
 
 int main(){
 	int i,T,x,y,z;
 	cin>>T;
	 while(T--){
	 	cin>>n>>m; for(i=1;i<=n;i++) g[i].clear();
	 	
 	for(i=1;i<=m;i++){
 	   cin>>x>>y>>z;
	   g[x].push_back(E(y,z)); if(z>=0) g[y].push_back(E(x,z));
	 } 
	 while(!q.empty()) q.pop();
 	cout<<(spfa(1)?"NO":"YES")<<endl; 
	 } 
 }