AC CODE:

#include<bits/stdc++.h>
#define int long long
using namespace std;
constexpr int N=1e5+5;
int n,m,root;
int dn,dfn[N],low[N],num,cnt,buc[N];
vector<int> e[N];
inline void fio(){
	ios::sync_with_stdio(0);
	#define endl '\n'
	cin.tie(0);cout.tie(0);
}
inline void tarjan(int u){
	dfn[u]=low[u]=++dn;
	int son=0;
	for(int v:e[u]){
		if(!dfn[v]){
			son++;
			tarjan(v);
			low[u]=min(low[u],low[v]);
			if(low[v]>=dfn[u]&&u!=root) cnt+=!buc[u],buc[u]=1;
		}
		else low[u]=min(low[u],dfn[v]);
	}
	if(son>=2&&u==root) cnt+=!buc[u],buc[u]=1;
}
signed main(){
	fio();
	cin>>n>>m;
	for(int i=1,u,v;i<=m;i++){cin>>u>>v;e[u].push_back(v);e[v].push_back(u);}
	for(int i=1;i<=n;i++){
		if(!dfn[i]) root=i,tarjan(i);
	}
	cout<<cnt<<endl;
	for(int i=1;i<=n;i++){
		if(buc[i]) cout<<i<<" ";
	}
	return 0;
}

WA code：

#include<bits/stdc++.h>
#define int long long
using namespace std;
constexpr int N=1e5+5;
int n,m,root;
int dn,dfn[N],low[N],num,cnt,buc[N];
vector<int> e[N];
set<int> st;
inline void fio(){
	ios::sync_with_stdio(0);
	#define endl '\n'
	cin.tie(0);cout.tie(0);
}
inline void tarjan(int u){
	dfn[u]=low[u]=++dn;
	int son=0;
	for(int v:e[u]){
		if(!dfn[v]){
			son++;
			tarjan(v);
			low[u]=min(low[u],low[v]);
			if(low[v]>=dfn[u]&&u!=root) st.insert(u);
		}
		else low[u]=min(low[u],dfn[v]);
	}
	if(son>=2&&u==root) st.insert(u);
}
signed main(){
	fio();
	cin>>n>>m;
	for(int i=1,u,v;i<=m;i++){cin>>u>>v;e[u].push_back(v);e[v].push_back(u);}
	for(int i=1;i<=n;i++){
		if(!dfn[i]) root=i,tarjan(i);
	}
	cout<<st.size()<<endl;
	for(auto x:st) cout<<x<<endl;
	return 0;
}