为何错误o(╥﹏╥)o

#include <bits/stdc++.h>
using namespace std;
const int N = 5e3+10;
int n,m;
struct node{
	int to,next,len;
}a[N];
int pre[N],k;
long long d[N];
int vis[N],cnt[N];
void add(int u,int v,int len){
	k++;
	a[k].to = v;
	a[k].next = pre[u];
	a[k].len = len;
	pre[u] = k;
}
bool spfa(){
	queue<int> q;
	for(int i = 1;i<=n;i++){
		d[i] = INT_MAX;
		vis[i] = 0;
	}
	q.push(0);
	d[0] = 0;
	vis[0] = 1;
	cnt[0] = 1;
	while(!q.empty()){
		int u = q.front();
		q.pop();
		vis[u] = 0;
		for(int i = pre[u];i;i = a[i].next){
			int to = a[i].to;
			if(d[to]>d[u]+a[i].len){
				d[to] = (long long)d[u]+a[i].len;
				if(vis[to]==0){
					vis[to] = 1;
					q.push(to);
					cnt[to]++;
					if(cnt[to]>n+1)return false;
				}
			}
		}
	}
	return true;
}
int main(){
	scanf("%d%d",&n,&m);
	int x,y,z;
	for(int i = 1;i<=m;i++){
		scanf("%d%d%d",&x,&y,&z);
		add(y,x,z);
	}
	for(int i = 1;i<=n;i++){
		add(0,i,0);
	}
	if(spfa()){
		for(int i = 1;i<=n;i++){
			printf("%d ",d[i]);
		}
	}else{
		printf("NO\n");
	}

	return 0;
}