HDU 4587 TWO NODES（割两个点的最大连通分支数）

  1 #include<iostream>
  2 #include<algorithm>
  3 #include<cstring>
  4 #include<cstdio>
  5 #include<sstream>
  6 #include<vector>
  7 #include<stack>
  8 #include<queue>
  9 #include<cmath>
 10 #include<map>
 11 #include<set>
 12 using namespace std;
 13 typedef long long ll;
 14 typedef pair<int,ll> pll;
 15 const int INF = 0x3f3f3f3f;
 16 const int maxn=5000+5;
 17 
 18 int n, m;
 19 int tot;
 20 int dfs_clock;
 21 int pre[maxn];
 22 int cut[maxn];
 23 int low[maxn];
 24 int head[2*maxn];
 25 int del;
 26 
 27 struct node
 28 {
 29     int v,next;
 30 }e[2*maxn];
 31 
 32 void addEdge(int u, int v)
 33 {
 34     e[tot].v=v;
 35     e[tot].next=head[u];
 36     head[u]=tot++;
 37 }
 38 
 39 int tarjan(int u, int fa)
 40 {
 41     int lowu=pre[u]=++dfs_clock;
 42     for(int i=head[u];i!=-1;i=e[i].next)
 43     {
 44         int v=e[i].v;
 45         if(v==del)  continue;
 46         if(!pre[v])
 47         {
 48             int lowv = tarjan(v,u);
 49             lowu=min(lowu,lowv);
 50             if(lowv>=pre[u])  cut[u]++;
 51         }
 52         else if(v!=fa)
 53             lowu=min(lowu,pre[v]);
 54     }
 55     if(fa<0)  cut[u]--;
 56     return low[u]=lowu;
 57 }
 58 
 59 int solve()
 60 {
 61     int cnt=0;
 62     dfs_clock=0;
 63     memset(cut,0,sizeof(cut));
 64     memset(pre,0,sizeof(pre));
 65     for(int i=0;i<n;i++)
 66     {
 67         if(del!=i && !pre[i])
 68         {
 69             cnt++;
 70             tarjan(i,-1);
 71         }
 72     }
 73     int ans=0;
 74     for(int i=0;i<n;i++)
 75     {
 76         if(i!=del) ans=max(ans,cnt+cut[i]);
 77     }
 78     return ans;
 79 }
 80 
 81 int main()
 82 {
 83     //freopen("in.txt","r",stdin);
 84     while(~scanf("%d%d",&n,&m))
 85     {
 86         tot=0;
 87         memset(head,-1,sizeof(head));
 88         for(int i=0;i<m;i++)
 89         {
 90             int u,v;
 91             scanf("%d%d",&u,&v);
 92             addEdge(u,v);
 93             addEdge(v,u);
 94         }
 95         int ans=-1;
 96         for(int i=0;i<n;i++)
 97         {
 98             del=i;
 99             ans=max(ans,solve());
100         }
101         printf("%d\n",ans);
102     }
103     return 0;
104 }