洛谷 P3388 【模板】割点（割顶）

#include <iostream>
#include <cstdio>
#include <stack>
#include <cstring>
using namespace std;
//Mystery_Sky
//
#define maxn 1000010
struct Edge{
	int to, next;
}edge[maxn];
int vis[maxn], low[maxn], dfn[maxn], cut[maxn];
int head[maxn], cnt, tot;
inline void add_edge(int u, int v)
{
	edge[++cnt].to = v;
	edge[cnt].next = head[u];
	head[u] = cnt;
}

void Tarjan(int u, int fa)
{
	int child = 0;
	low[u] = dfn[u] = ++tot;
	vis[u] = 1;
	for(int i = head[u]; i; i = edge[i].next) {
		int v = edge[i].to;
		if(!dfn[v]) {
			Tarjan(v, fa);
			low[u] = min(low[u], low[v]);
			if(low[v] >= dfn[u] && u != fa) cut[u] = 1;
			if(u == fa) child++;
		}
		low[u] = min(low[u], dfn[v]);
	}
	if(child >= 2 && u == fa) cut[u] = 1;
} 
int ans, n, m;
int main() {
	scanf("%d%d", &n, &m);
	int u, v;
	for(int i = 1; i <= m; i++) {
		scanf("%d%d", &u, &v);
		add_edge(u, v);
		add_edge(v, u);
	}
	for(int i = 1; i <= n; i++) {
		if(!dfn[i]) Tarjan(i, i);
		if(cut[i]) ++ans;
	}
	printf("%d\n", ans);
	for(int i = 1; i <= n; i++)
		if(cut[i]) printf("%d ", i);
	return 0;
}