spfa【模板】

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;
struct edge{
    int to;
    int next;
    int len;
}qwq[100005];
queue<int>pq;
int edge_cnt=0,n,m,head[100005],in[100005],stk[100005],dist[100005];
bool spfa()
{
    memset(in,0,sizeof(in));
    memset(stk,0,sizeof(stk));
    memset(dist,-1,sizeof(dist));
    dist[0]=0;
    while(!pq.empty())
    {
        pq.pop();
    }
    pq.push(0);
    in[0]++;
    stk[0]=1;
    while(!pq.empty())
    {
        int qaq=pq.front();pq.pop();
        stk[qaq]=0;
        for(int i = head[qaq];i!=-1;i=qwq[i].next)
        {
            int v=qwq[i].to;
            if(dist[v]<dist[qaq]+qwq[i].len)
            {
                dist[v]=dist[qaq]+qwq[i].len;
                if(!stk[v])
                {
                    pq.push(v);
                    in[v]++;
                    stk[v]=1;
                    if(in[v]>n+1){
                        return false;
                    }
                }
            }
        }
    }
    return true;
}
void add(int x,int y,int z)
{
    qwq[edge_cnt].to=y;
    qwq[edge_cnt].next=head[x];
    qwq[edge_cnt].len=z;
    head[x]=edge_cnt++; 
}
int main()
{
        scanf("%d%d",&n,&m);
           memset(head,-1,sizeof(head));
         edge_cnt=0;
        for(int i = 0 ; i < m ;i++)
        {
            int a,b,c;
             scanf("%d%d%d",&a,&b,&c);
            add(a,b,c);
         }
     if(!spfa())printf("-1
");
    return 0;
 }