连通性问题

求割点

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll N=2e4+10;
ll n,m,dfn[N],low[N],tot,root;
bool cut[N];
vector<ll> G[N];
void tarjan(ll u){
	dfn[u]=low[u]=++tot;
	ll flag=0;
	for(auto v:G[u]){
		if(!dfn[v]){
			tarjan(v),low[u]=min(low[u],low[v]);
			if(low[v]>=dfn[u]){
				flag++;
				if(u!=root||flag>1)cut[u]=true;
			}
		}else low[u]=min(low[u],dfn[v]);
	}
}
int main(){
	cin >> n >> m;
	for(ll i=1;i<=m;i++){
		ll u,v;
		cin >> u >> v;
		G[u].push_back(v);
		G[v].push_back(u);
	}
	for(ll i=1;i<=n;i++)if(!dfn[i])root=i,tarjan(i);
	vector<ll> ans;
	for(ll i=1;i<=n;i++)if(cut[i])ans.push_back(i);
	cout << ans.size() << endl;
	for(auto i:ans)cout << i << ' ';
	return 0;
}