poj 3694 Network（双连通分量）

题目：http://poj.org/problem?id=3694

 #include <iostream>
 #include <cstring>
 #include <cstdio>
 #include <cstdlib>
 #include <algorithm>
 #include <vector>
 using namespace std;
 const int MAXN=;
 int bin[MAXN],n,m;
 int low[MAXN],dfn[MAXN],father[MAXN];
 int q,cut,index;
 vector<int>g[MAXN];

 int findx(int x)
 {
     return bin[x]==x?x:(bin[x]=findx(bin[x]));
 }
 int merge(int x,int y)
 {
     int fx,fy;
     fx=findx(x);
     fy=findx(y);
     if(fx!=fy)
     {
         bin[fx]=fy;
         return ;
     }
     else
         return ;
 }

 void tarjan(int i,int pre)
 {
     int j,k;
     low[i]=dfn[i]=++index;
     for (k=; k<g[i].size(); k++)
     {
         j = g[i][k];
         if (!dfn[j])
         {
             tarjan(j,i);
             low[i]=min(low[i],low[j]);
             father[j]=i;
             if (low[j] > dfn[i])
                 cut++;
             else
                 merge(i,j);
         }
         else if (j!=pre)
         {
             low[i]=min(low[i],dfn[j]);
         }
     }
 }
 void lca(int u,int v)
 {
     while (u!=v)
     {
         while (dfn[u]>=dfn[v] && u!=v)
         {
             if (merge(u,father[u]))
                 cut--;
             u = father[u];
         }
         while (dfn[v]>=dfn[u]&&u!=v)
         {
             if (merge(v,father[v]))
                 cut--;
             v=father[v];
         }
     }
 }

 int main()
 {
     int i,x,y,T=;
     while(~scanf("%d%d",&n,&m)&&n||m)
     {
         for(i=; i<=n+; i++)
         {
             g[i].clear();
             low[i]=dfn[i]=father[i]=;
             bin[i]=i;
         }
         index=cut=;

         for(i=; i<m; i++)
         {
             scanf("%d%d",&x,&y);
             g[x].push_back(y);
             g[y].push_back(x);
         }
         tarjan(,-);
         scanf("%d",&q);

         printf("Case %d:\n",T++);
         while(q--)
         {
             scanf("%d%d",&x,&y);
             lca(x,y);
             printf("%d\n",cut);
         }
         cout<<endl;
     }
     return ;
 }