求助

#include<iostream>
#include<cstdio>
#include<queue>
#include<climits>
using namespace std;

const int MAXN = 20005,MAXM = 100010,INF = INT_MAX;
int t,n,m,x,y,z,cnt,head[MAXN],dis[MAXN],cont[MAXN],crt,beu;
bool inq[MAXN];

struct Edge {
	int to;
	int w;
	int nxt;
} l[MAXM*2];

void addEdge(int x,int y,int z){
	cnt++;
	l[cnt].to = y;
	l[cnt].w = z;
	l[cnt].nxt = head[x];
	head[x] = cnt;
} 
bool spfa(){
	queue<int> q;
	crt = 1;
	q.push(crt);
	inq[crt] = true;
	dis[crt] = 0;
	cont[crt] = 1;
	while(q.size()){
		crt = q.front();
		q.pop();
		inq[crt] = false;
		for(int i=head[crt];i;i=l[i].nxt){
			beu = l[i].to;
			if(dis[beu] > (dis[crt] + l[i].w)){
				dis[beu] = dis[crt] + l[i].w;
				if(!inq[beu]){
					q.push(beu);
					inq[beu] = true;
				}
				cont[beu] = cont[crt] + 1;
				if(cont[beu] >= n){
					return true;
				}
			}
		}
	}
	return false;
}
void init(){
	cnt = 0;
	for(int i=1;i<=n;i++){
		head[i] = cont[i] = 0;
		dis[i] = INF;
		inq[i] = false;
	}
}

int main(void){
	//得到数据的组数
	scanf("%d",&t);
	for(int i=1;i<=t;i++){
		init();
		//得到这组数据的点数和边数
		scanf("%d%d",&n,&m);
		for(int j=1;j<=m;j++){
			scanf("%d%d%d",&x,&y,&z);
			addEdge(x,y,z);
			if(z >= 0){
				addEdge(y,x,z);
			}
		}
		if(spfa()){
			printf("YE5\n");
		}else{
			printf("N0\n");
		}
	} 
	return 0;
}