POJ——T2117 Electricity

 http://poj.org/problem?id=2117

Time Limit: 5000MS		Memory Limit: 65536K
Total Submissions: 5459		Accepted: 1788

当m==0 时，特判输出 n-1~~~

先求出原始的连通分量，

然后只有删割点才会增加连通分量，枚举每个割点

最后加上原始的

 #include <algorithm>
 #include <cstring>
 #include <cstdio>

 using namespace std;

 const int N();
 int n,m,u,v;
 int sumedge,head[N<<];
 struct Edge
 {
     int to,next;
     Edge(int to=,int next=) :
         to(to),next(next) {}
 }edge[N*];

 void ins(int from,int to)
 {
     edge[++sumedge]=Edge(to,head[from]);
     head[from]=sumedge;
 }

 int low[N<<],dfn[N<<],tim;
 int sumcol,num[N];
 int cutpoint[N];

 void DFS(int now,int pre)
 {
     low[now]=dfn[now]=++tim;
     int sumtredge=,if_cutpoint=;
     for(int i=head[now];i!=-;i=edge[i].next)
     {
         int go=edge[i].to;
         if((i^)!=pre)
         {
             if(!dfn[go])
             {
                 sumtredge++;
                 DFS(go,i);
                 if(low[go]>=dfn[now])
                 {
                     if_cutpoint=;
                     num[now]++;
                 }

                 low[now]=min(low[now],low[go]);
             }
             else low[now]=min(low[now],dfn[go]);
         }
     }
     if(pre==-)
     {
         if(sumtredge>)  cutpoint[now]=;
     }
     else if(if_cutpoint) cutpoint[now]=;
 }

 int ans,cnt,tmp,vis[N],root[N],cut[N];

 void link(int x)
 {
     vis[x]=;
     for(int i=head[x];i!=-;i=edge[i].next)
     {
         v=edge[i].to;
         if(!vis[v]) link(v);
     }
 }

 void cut_point(int pre,int fa)
 {
     vis[pre]=;
     for(int i=head[pre];i!=-;i=edge[i].next)
     {
         int go=edge[i].to;
         if(!vis[go])
         {
             if(pre==fa) cnt++;
             cut_point(go,fa);
         }
     }
 }

 void init(int n)
 {
     sumedge=-; ans=tim=tmp=cnt=;
     memset(vis,,sizeof(vis));
     memset(low,,sizeof(low));
     memset(dfn,,sizeof(dfn));
     memset(num,,sizeof(num));
     memset(cut,,sizeof(cut));
     memset(root,,sizeof(root));
     memset(head,-,sizeof(head));
     memset(cutpoint,,sizeof(cutpoint));
 }

 int main()
 {
 //    freopen("makerout.txt","r",stdin);
 //    freopen("myout.txt","w",stdout);

     while(~scanf("%d%d",&n,&m)&&n)
     {
         init(n);
         if(m==) printf("%d\n",n-);
         else
         {
             for(;m;m--)
             {
                 scanf("%d%d",&u,&v);
                 ins(u,v); ins(v,u);
             }
             for(int i=;i<n;i++)
                 if(!vis[i]) ++tmp,link(i);
             for(int i=;i<n;i++)
                 if(!dfn[i]) DFS(i,-);
             for(int i=;i<n;i++)
                 if(cutpoint[i])
                 {
                     memset(vis,,sizeof(vis));
                     cut_point(i,i);
                     ans=max(ans,cnt-);
                     cnt=;
                 }
             ans+=tmp;
             printf("%d\n",ans);
         }
     }
     return ;
 }