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点双/边双连通分量

点双

找到割点后一直退栈

http://ybt.ssoier.cn:8088/problem_show.php?pid=1521

include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include<stack>
using namespace std ;
 
 const int N=502;
 #define int long long
  
 vector<int> g[N],bk[N];
 stack<int> st; 
 int n,m,low[N],dfn[N],cut[N],pool,tot;
  
 void add(int x,int y){
    g[x].push_back(y);
 }
 void init(){
        int i,x,y;
        for(i=0;i<N;i++) g[i].clear(),cut[i]=dfn[i]=low[i]=0; 
        pool=tot= 0;
        while(!st.empty()) st.pop();
         
        for(i=1;i<=m;i++){
            cin>>x>>y;
            n=max(n,max(x,y));
            add(x,y),add(y,x);
        }   
}
 void dfs(int x,int fa){
    dfn[x]=low[x]=++pool; st.push(x);
       
      int c=0;
    for(int y:g[x]){
      if(!dfn[y]){
        c++;
        dfs(y,x),low[x]=min(low[x],low[y]);
        if(!fa&&c>1||fa&&dfn[x]<=low[y]) cut[x]=1;
         
        if(dfn[x]<=low[y]){
            tot++; bk[tot].clear();
             
            while(1){
              int t=st.top(); st.pop(); 
              bk[tot].push_back(t);
              if(t==y) break;
            } 
           bk[tot].push_back(x);
        }
      } 
      else low[x]=min(low[x],dfn[y]);
    }
 }
  
 
 void sov(){
    for(int i=1;i<=n;i++) 
            if(!dfn[i]) dfs(i,0); 
    int c1=0,c2=1;
     
    for(int i=1;i<=tot;i++){
        int cnt=0, siz=bk[i].size(); 
         
        for(int x:bk[i])
            if(cut[x]) cnt++;
           
        if(cnt==0) c1+=2, c2=c2*siz*(siz-1)/2;
        if(cnt==1) c1++, c2=c2*(siz-1);
    }
   cout<<c1<<' '<<c2<<'\n'; 
 }
signed main(){
    int T=0;
    while(cin>>m&&m){
        init(); 
        cout<<"Case "<<++T<<": ";
        sov();
    }
 }

边双

　https://vjudge.csgrandeur.cn/problem/POJ-3352

#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include<stack>
using namespace std ;
 
 const int N=1e5;
 #define int long long
  
 vector<int> g[N];
 
 int n,m,low[N],dfn[N],pool;
  
 void add(int x,int y){ g[x].push_back(y); }
  
 void dfs(int x,int fa){
    dfn[x]=low[x]=++pool; 
       
    for(int i=0;i<g[x].size();i++){
          int y =g[x][i]; if(fa==y) continue ;
          if(!dfn[y]){
             dfs(y,x) ; low[x] =min(low[x],low[y]) ;
          } 
          else if(dfn[x]>dfn[y]) low[x]=min(low[x],dfn[y]);
    }
 }
  
  
int in[N] ;
 void sov(){
    for(int i=1;i<=n;i++) 
        if(!dfn[i]) dfs(i,0); 
     
    for(int i=1;i<=n;i++)
         for(int e=0;e<g[i].size();e++){
            int y= g[i][e] ;
            if(low[i]!=low[y]) in[low[y]]++;
         }
         
    int cnt=0 ;
    for(int i=1;i<=n;i++)
        if(in[i]==1) cnt++ ;
    cout <<(cnt+1)/2<<endl;
 }
signed main(){
        cin>>n>>m;
        for(int x,y,i=1;i<=m;i++){
            cin>>x>>y;
            add(x,y),add(y,x);
        }   
        sov() ;
 }