割点（模板）

https://www.luogu.com.cn/problem/P3388

#include<bits/stdc++.h>
#define lc p<<1
#define rc p<<1|1
#define INF 1e18
using namespace std;
#define lowbit(x) x&(-x)
#define endl '\n'
using ll = long long;
using int128 = __int128;
using pii = pair<ll,ll>;
const double PI = acos(-1);
const int N=2e4+10;
int dfn[N],low[N],tot;
bool cut[N];
int root;
vector<int> e[N*2];
void tarjan(int u){
	dfn[u]=low[u]=++tot;
	int child=0;
	for(auto v:e[u]){
		if(!dfn[v]){
			tarjan(v);
			low[u]=min(low[u],low[v]);
			if(low[v]>=dfn[u]){
				child++;
				if(u!=root||child>=2){
					cut[u]=1;
				}
			}
		}
		else{
			low[u]=min(low[u],dfn[v]);
		}
	}
}
void solve(){
	int n,m;cin>>n>>m;
	for(int i=1;i<=m;i++){
		int u,v;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);
		}
	}
	vector<int> ans;
	for(int i=1;i<=n;i++){
		if(cut[i]){
			ans.push_back(i);
		}
	}
	cout<<ans.size()<<endl;
	for(auto t:ans){
		cout<<t<<" ";
	}
}


int main() {
//	ios::sync_with_stdio(false);
//	cin.tie(nullptr), cout.tie(nullptr);
	
	int T = 1;
//	cin>>T;
	while (T--) {
		solve();
	}
	
	return 0;
}