POJ 1144 无向图的割点

 1 //无向图的割点
 2 #include<algorithm>
 3 #include<cstdio>
 4 #include<cstring>
 5 #include<cstdlib>
 6 #include<iostream>
 7 #include<queue>
 8 #include<vector>
 9 #include<stack>
10 using namespace std;
11 const int maxn=107;
12 int n;
13 vector<int> G[maxn];
14 int ans,low[maxn],pre[maxn],sum,root;
15 bool iscut[maxn];
16 void dfs(int u,int fa)
17 {
18     int lowu;
19     low[u]=pre[u]=sum++;
20     int l=G[u].size();
21     int child=0;
22     for(int i=0;i<l;i++)
23     {
24         int v=G[u][i];
25         if(!pre[v]){
26             child++;
27             dfs(v,u);
28             low[u]=min(low[u],low[v]);
29             if(u==root&&child==2) iscut[u]=1;
30             if(low[v]>=pre[u]&&u!=root){
31                 iscut[u]=1;
32             }
33         }
34         else if(u!=v)
35         {
36             low[u]=min(low[u],pre[v]);
37         }
38     }
39 }
40 int main()
41 {
42     char c;int m,a,b;
43     while(1){
44         scanf("%d",&n);
45         if(n==0) break;
46         for(int i=0;i<maxn;i++) G[i].clear();
47         while(1){
48             scanf("%d",&m);
49             if(m==0) break;
50              while((c=getchar())!=‘\n‘)
51             {
52                 scanf("%d",&b);
53                 G[m].push_back(b);
54                 G[b].push_back(m);
55             }
56         }
57         memset(pre,0,sizeof(pre));
58         memset(iscut,0,sizeof(iscut));
59         memset(low,0,sizeof(low));
60         ans=0,sum=1,root=1;
61         if(n==1||n==2){printf("0\n");continue;}
62         dfs(1,-1);
63         for(int i=0;i<=n;i++) if(iscut[i]) ans++;
64         printf("%d\n",ans);
65     }
66 }