P3388 玄关求条

#include<bits/stdc++.h>
using namespace std;
const int N=1e5+5;
int n,m,dfn[N],low[N],idx,res,v;
bool vis[N],flag[N];
vector<int>bian[N];
void Tarjan(int u,int fa){
	vis[u]=1;
	low[u]=dfn[u]=++idx;
	int child=0;
	for(int i=0;i<bian[u].size();i++){
		v=bian[u][i];
		if(!vis[v]){
			child++;
			Tarjan(v,u);
			low[u]=min(low[u],low[v]);
			if(fa!=u&&low[v]>=dfn[u]&&!flag[u]){
				flag[u]=true;
				res++;
			}
		}else if(v!=fa){
			low[u]=min(low[u],dfn[v]);
		}
	}
	if(fa==u&&child>=2&&!flag[u]){
		flag[u]=true;
		res++;
	}
}

int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin>>n>>m;
	for(int i=1;i<=m;i++){
		int x,y;
		cin>>x>>y;
		bian[x].push_back(y);
		bian[y].push_back(x);
	}
	for(int i=1;i<=n;i++)
		if(!vis[i]){
			idx=0;
			Tarjan(i,i);
		}
	cout<<res<<endl;
	for(int i=1;i<=n;i++)if(flag[i])cout<<i<<' ';
	return 0;
}