保龄求助

#include<cmath>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define N 21234
using namespace std;
struct Edge {
	int to,head;
} edge[10*N];
int dfn[N],low[N],cnt[N],ord,stk[N],ned,tot,ifs[N],vis[N],gd[N],n,m,u,v,ans;
void add(int u,int v) {
	edge[++ned].to=v;
	edge[ned].head=cnt[u];
	cnt[u]=ned;
}
void Empty() {
	memset(gd,0,sizeof(gd));
	memset(dfn,0,sizeof(dfn));
	memset(low,0,sizeof(low));
	memset(stk,0,sizeof(stk));
	memset(cnt,0,sizeof(cnt));
	memset(ifs,0,sizeof(ifs));
	memset(vis,0,sizeof(vis));
	memset(edge,0,sizeof(edge));
	ans=ned=ord=tot=0;
}
void Tarjan(int u,int fa) {
	int chi=0;
	dfn[u]=low[u]=++ord;
	stk[++tot]=u;
	vis[u]=ifs[u]=1;
	for (int i=cnt[u]; i; i=edge[i].head) {
		int v=edge[i].to;
		if (!vis[v]) {
			++chi;
			Tarjan(v,fa);
			low[u]=min(low[u],low[v]);
		} else if (ifs[v]) {
			low[u]=min(low[u],dfn[v]);
		}
	}
	if (chi>=2&&u==fa) gd[++ans]=u;
	else if (low[u]==dfn[u]) {
		int v=stk[tot];
		while (v!=u) {
			ifs[v]=0;
			v=stk[--tot];
		}
		gd[++ans]=u;
	}
}
int main() {
	Empty();
	scanf("%d%d",&n,&m);
	for (int i=1; i<=m; ++i) {
		scanf("%d%d",&u,&v);
		add(u,v);
		add(v,u);
	}
	for (int i=1; i<=n; ++i)
		if (!vis[i]) Tarjan(i,i);
	sort(gd+1,gd+ans+1);
	printf("%d\n",ans);
	for (int i=1; i<=ans; ++i)
		printf("%d ",gd[i]);
	return 0;
}