Find articulation points

#include <bits/stdc++.h>

using namespace std;

vector<vector<pair<int, int>>> g;
vector<bool> used;
vector<int> tin;
vector<int> tup;
int timer = 0;
set<int> ans;
vector<int> cnt;

void dfs(int v, int ind) {
    used[v] = 1;
    tin[v] = timer++;
    tup[v] = tin[v];
    int ch = 0;
    for(int i = 0; i < g[v].size(); i++) {
        int to = g[v][i].first;
        if(g[v][i].second == ind) continue;
        if(!used[to]) { // прямое
            dfs(to, g[v][i].second);
            tup[v] = min(tup[v], tup[to]);
            ch++;
            if(tin[v] <= tup[to]) {
                ans.insert(v);
            }
            cnt[v]++;
        }
        else {  // обратное
            tup[v] = min(tup[v], tin[to]);
        }
    }
}

int main() {
    int n, m;
    cin >> n >> m;
    g.resize(n);
    tin.resize(n);
    tup.resize(n);
    used.resize(n);
    cnt.resize(n);
    for(int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        if(a > b) {
            swap(a, b);
        }
        a--;
        b--;
        g[a].push_back({b, i});
        g[b].push_back({a, i});
    }
    for(int i = 0; i < n; i++) {
        if(!used[i]) {
            dfs(i, i);
        }
    }
    cout << ans.size() - (cnt[0] < 2) << '\n';
    for(auto i : ans) {
        if(i == 0 && cnt[0] < 2) continue;
        cout << i + 1 << ' ';
    }
}