[双连通分量] POJ 3177 Redundant Paths

#include<stdio.h>
#include<string.h>
struct mp
  {
  	 int begin,to,next;
  }map[10010];
int frist[10010],num,dfn[10010],low[10010],times,bridgenum,father[10010];
int degree[10010],con[10010],stack[10010],cnt,top,s[10010];
bool count[10010];
void init()
  {
  	 memset(father,0,sizeof(father));
  	 memset(count,0,sizeof(count));
  	 memset(con,0,sizeof(con));
  	 memset(degree,0,sizeof(degree));
  	 memset(s,0,sizeof(s));
  	 memset(stack,0,sizeof(stack));
  	 memset(frist,0,sizeof(frist));
  	 memset(dfn,0,sizeof(dfn));
  	 memset(low,0,sizeof(low));
  	 memset(map,0,sizeof(map));
  	 num=times=bridgenum=cnt=top=0;
  }
void add(int x,int y)
   {
   	 ++num;
   	 map[num].begin=x;map[num].to=y;
	 map[num].next=frist[x];frist[x]=num;
   	 return;
   }
void tarjian(int v)
  {
  	 int i;bool flag=true;
  	 dfn[v]=low[v]=++times;
  	 stack[top++]=v;
  	 for(i=frist[v];i;i=map[i].next)
  	   {
  	   	  if(map[i].to==father[v]&&flag)
  	   	    {
  	   	       flag=false;
  	   	       continue;
			}
  	   	  if(!dfn[map[i].to])
  	   	    {
  	   	       father[map[i].to]=v;
  	   	       tarjian(map[i].to);
  	   	       if(low[map[i].to]<low[v]) low[v]=low[map[i].to];
			}
		  else 
		  if(dfn[map[i].to]<low[v]) low[v]=dfn[map[i].to];
	   }
	   if(low[v]==dfn[v])
	     {
	     	++cnt;
	     	do
	     	{
	     	  v=stack[--top];
	     	  s[v]=cnt;
			}while(dfn[v]!=low[v]);
		 }
  }
int main()
  {
  	 int n,m,a,b,i,u,v,k=0,ans=0,j;
  	 init();
  	 scanf("%d%d",&n,&m);
  	 for(i=0;i<m;++i)
  	   {
  	   	  scanf("%d%d",&a,&b);
  	   	  add(a,b);add(b,a);
	   }
	 tarjian(1);
	 for(i=1;i<=n;++i)
	   {
	   	  for(j=frist[i];j;j=map[j].next)
	   	  {
	   	  v=map[j].to;
	   	  if(s[i]!=s[v])
	   	   {
	   	   	  ++degree[s[i]];
	   	   	  ++degree[s[v]];
		   }
	      }
	   }
	 for(i=1;i<=cnt;++i) 
	    if(degree[i]==2) 
		    ++ans;
	 printf("%d\n",(ans+1)/2);
  	 return 0;
  }