HDU-4587-tarjin/割点

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<vector>
 4 #include<cstring>
 5 using namespace std; 
 6 #define LL long long 
 7 #define pb push_back
 8 const int maxn=5010;
 9 vector<int>g[maxn];
10 int dfn[maxn],low[maxn],sub[maxn],root,sum,ban;
11 bool vis[maxn];
12 void dfs(int u){
13     dfn[u]=low[u]=sum++;
14     vis[u]=1;
15     int son=0;
16     for(int i=0;i<g[u].size();++i){
17         int v=g[u][i];
18         if(v==ban)continue;
19         if(vis[v]){
20             low[u]=min(low[u],dfn[v]);
21         }
22         else{
23             dfs(v);
24             if(u==root)son++;
25             else{
26                 if(low[v]>=dfn[u])sub[u]++;
27             }
28             low[u]=min(low[u],low[v]);
29         }
30     }
31     if(u==root)sub[u]=son;
32     else sub[u]++;
33 }
34 int main(){
35     int i,j,u,v,n,m;
36     while(scanf("%d%d",&n,&m)==2){
37         for(i=0;i<n;++i){
38             vis[i]=sub[i]=0;
39             g[i].clear();
40         }
41         while(m--){
42             scanf("%d%d",&u,&v);
43             g[u].pb(v);
44             g[v].pb(u);
45         }
46         int ans=0;
47         for(i=0;i<n;++i){
48             ban=i;
49             int p=0;
50             sum=0;
51             memset(vis,0,sizeof(vis));
52             memset(sub,0,sizeof(sub));
53             for(j=0;j<n;++j){
54                 if(j==ban||vis[j])continue;
55                 root=j;
56                 dfs(j);
57                 p++;
58             }
59             for(j=0;j<n;++j){
60                 if(j==ban)continue;
61                 if(ans<sub[j]+p-1) ans=sub[j]+p-1;
62             }
63         }
64         printf("%d\n",ans);
65     }
66     return 0;
67 }