【模板】割点 tarjan

//tarjan割点
#include <bits/stdc++.h>
using namespace std;
const int M = 250000;
struct E{int v,nxt;};
E edge[M];
int n,m,head[M],dfn[M],low[M],cnt,bo[M];
int ans;
void tarjan(int u,int fa){
	dfn[u] = low[u] = ++cnt;
	int child = 0; 
	for(int v,i=head[u];i;i=edge[i].nxt){
		v = edge[i].v;
		if(!dfn[v]){
			tarjan(v,fa);
			low[u] = min(low[u],low[v]);
			if(low[v]>=dfn[u]&&u!=fa){
				bo[u] = 1;
			}
			if(u==fa)
			child++;
		}else low[u] = min(low[u],dfn[v]);	
	} 
	if(child>=2)bo[fa]=1;
	
}
int main()
{
	scanf("%d %d",&n,&m);
	int ccnt = 0;
	for(int i=1;i<=m;i++){
		int u,v;
		scanf("%d %d",&u,&v);
		ccnt++; edge[ccnt].v = v; edge[ccnt].nxt = head[u]; head[u]=ccnt;
		ccnt++; edge[ccnt].v = u; edge[ccnt].nxt = head[v]; head[v]=ccnt;	
	}
	for(int i=1;i<=n;i++)
		if(!dfn[i])
			tarjan(i,i);
	for(int i=1;i<=n;i++)if(bo[i])ans++; 
	printf("%d\n",ans);
	for(int i=1;i<=n;i++)
	if(bo[i])printf("%d ",i);
	return 0;
 }