【洛谷P3385】模板-负环

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 using namespace std;
 5 const int N=200010,M=400010;
 6 int n,m,size,sg,vis[N],d[N];
 7 int head[M],to[M],nxt[M],val[M];
 8 void uni(int x,int y,int z){
 9     size++;
10     nxt[size]=head[x];
11     head[x]=size;
12     to[size]=y;
13     val[size]=z;
14 }
15 void dfs_spfa(int x){
16     if (sg) return;
17     vis[x]=1;
18     for (int k=head[x];k;k=nxt[k]){
19         if (sg) return;
20         int y=to[k];
21         if (d[x]+val[k]<d[y]){
22             d[y]=d[x]+val[k];
23             if (vis[y]){
24                 sg=1;
25                 return;
26             }
27             else
28                 dfs_spfa(y);
29         }
30     }
31     vis[x]=0;
32 }
33 int main(){
34     int a,b,w,T;
35     scanf("%d",&T);
36     while (T--){
37         size=sg=0;
38         scanf("%d %d",&n,&m);
39         memset(d,0,sizeof(d));
40         memset(head,0,sizeof(head));
41         memset(vis,0,sizeof(vis));
42         for (int i=1;i<=m;i++){
43             scanf("%d %d %d",&a,&b,&w);
44             uni(a,b,w);
45             if (w>=0) uni(b,a,w);
46         }
47         for (int i=1;i<=n;i++){
48             dfs_spfa(i);
49             if (sg) break;
50         }
51         if (sg) printf("YE5\n");
52         else printf("N0\n");
53     }
54     return 0;
55 }