hdu 1269 迷宫城堡 (强连通入门题）

 1 /******************************************************
 2        迷宫城堡(hdu 1269)
 3        强连通入门题
 4 
 5 ******************************************************/
 6 
 7 
 8 #include<cstdio>
 9 #include<cstring>
10 #include<algorithm>
11 #include<stack>
12 #include<vector>
13 using namespace std;
14 
15 const int mx=10005;
16 stack<int>s;
17 vector<int>g[mx];
18 int dfn[mx],low[mx];
19 int sccno[mx],vs[mx];///sccno记录每个节点是第几个强连通分量
20 int cut_dfs,cut_scc; ///cut_dfn记录dfs每个节点遍历循序，
21                      ///cut_scc记录强连通分量的个数
22 
23 void dfs(int u)
24 {
25     s.push(u);
26     vs[u]=1;
27     dfn[u]=low[u]=++cut_dfs;
28     for (int i=0;i<g[u].size();i++)
29     {
30         int v=g[u][i];
31         if (!vs[v])
32         {
33             dfs(v);
34             low[u]=min(low[u],low[v]);
35         }
36         else low[u]=min(low[u],dfn[v]);
37     }
38     if (low[u]==dfn[u])
39     {
40         cut_scc++;
41         while (1)
42         {
43             int x=s.top();
44             s.pop();
45             sccno[x]=cut_scc;
46             if (x==u) break;
47         }
48     }
49 }
50 
51 int main()
52 {
53     int n,m,a,b;
54     while (~scanf("%d%d",&n,&m)&&n+m)
55     {
56         for (int i=1;i<=n;i++) g[i].clear();
57         while (m--)
58         {
59             scanf("%d%d",&a,&b);
60             g[a].push_back(b);
61         }
62         while (!s.empty()) s.pop();
63         cut_dfs=cut_scc=0;
64         memset(dfn,0,sizeof(dfn));
65         memset(low,0,sizeof(low));
66         memset(vs,0,sizeof(vs));
67         for (int i=1;i<=n;i++)
68         {
69             if (!dfn[i]) dfs(i);
70         }
71         if (cut_scc==1) printf("Yes
");
72         else printf("No
");
73     }
74 }