https://www.luogu.com.cn/record/152373498

#include <iostream>
#include <vector>
#include <algorithm>

struct Node // 结点
{
    int dfn, low;
};

int node_cnt; // 用来求 dfn
Node vt[20005]; // 点集
std::vector<int> ans; // 割点
std::vector<int> eg[20005]; // 边集

void tarjan(int u, int fa)
{
    int son_cnt = 0; // 儿子数, 为根作特判
    vt[u].dfn = vt[u].low = ++node_cnt;
    for (auto v : eg[u])
        if (v != fa)
        {
            if (vt[v].dfn == 0)
            {
                tarjan(v, u);
                vt[u].low = std::min(vt[u].low, vt[v].low);
                if (vt[v].low >= vt[u].dfn)
                {
                    son_cnt++;
                    if (fa != 0 || son_cnt > 1) // fa != 0 即这个点非根
                        ans.push_back(u);
                }
            }
            else
                vt[u].low = std::min(vt[u].low, vt[v].dfn);
        }
}

int main()
{
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    std::cout.tie(nullptr);

    int n, m;

    std::cin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int x, y;
        std::cin >> x >> y;
        eg[x].push_back(y);
        eg[y].push_back(x);
    }

    for (int i = 1; i <= n; i++)
        if (vt[i].dfn == 0)
            tarjan(i, 0);

    std::sort(ans.begin(), ans.end());

    std::cout << ans.size() << "\n";
    for (auto u : ans)
        std::cout << u << " ";
    std::cout << "\n";

    return 0;
}