spfa【模板】

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