spfa【模板】

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<queue>
 5 using namespace std;
 6 struct edge{
 7     int to;
 8     int next;
 9     int len;
10 }qwq[100005];
11 queue<int>pq;
12 int edge_cnt=0,n,m,head[100005],in[100005],stk[100005],dist[100005];
13 bool spfa()
14 {
15     memset(in,0,sizeof(in));
16     memset(stk,0,sizeof(stk));
17     memset(dist,-1,sizeof(dist));
18     dist[0]=0;
19     while(!pq.empty())
20     {
21         pq.pop();
22     }
23     pq.push(0);
24     in[0]++;
25     stk[0]=1;
26     while(!pq.empty())
27     {
28         int qaq=pq.front();pq.pop();
29         stk[qaq]=0;
30         for(int i = head[qaq];i!=-1;i=qwq[i].next)
31         {
32             int v=qwq[i].to;
33             if(dist[v]<dist[qaq]+qwq[i].len)
34             {
35                 dist[v]=dist[qaq]+qwq[i].len;
36                 if(!stk[v])
37                 {
38                     pq.push(v);
39                     in[v]++;
40                     stk[v]=1;
41                     if(in[v]>n+1){
42                         return false;
43                     }
44                 }
45             }
46         }
47     }
48     return true;
49 }
50 void add(int x,int y,int z)
51 {
52     qwq[edge_cnt].to=y;
53     qwq[edge_cnt].next=head[x];
54     qwq[edge_cnt].len=z;
55     head[x]=edge_cnt++; 
56 }
57 int main()
58 {
59         scanf("%d%d",&n,&m);
60            memset(head,-1,sizeof(head));
61          edge_cnt=0;
62         for(int i = 0 ; i < m ;i++)
63         {
64             int a,b,c;
65              scanf("%d%d%d",&a,&b,&c);
66             add(a,b,c);
67          }
68      if(!spfa())printf("-1
");
69     return 0;
70  }