不需要初始化距离，将每个点都加入队列，记录一个cnt数组

#include<bits/stdc++.h>
using namespace std;
const int N = 2010;
const int M = 1e4+10;
int val[M],ne[M],h[N],w[M],idx;
int cnt[N],dist[N];
int n,m;
bool st[N];

void add(int a,int b,int weight)
{
    val[idx] = b;
    ne[idx] = h[a];
    w[idx] = weight;
    h[a] = idx++;
}

bool spfa()
{
    queue<int> q;
    for(int i = 1;i<=n;i++)
    {
        q.push(i);
        st[i] = true;
    }

    while(q.size())
    {
        int t = q.front();
        q.pop();
        st[t] = false;
        for(int i = h[t];~i;i = ne[i])
        {
            int j = val[i];
            if(dist[j] > dist[t] + w[i])
            {
                dist[j] = dist[t] + w[i];
                cnt[j] = cnt[t] + 1;
                if(cnt[j] >= n)return true;
                if(!st[j])
                {
                    q.push(j);
                    st[j] = true;
                }
            }
        }
    }
    return false;
}
int main()
{
    cin>>n>>m;
    memset(h,-1,sizeof h);
    while (m -- )
    {
        int a,b,c;
        cin>>a>>b>>c;
        add(a,b,c);
    }
    if(spfa())puts("Yes");
    else puts("No");
    return 0;
}