Задача C. Points. Точки сочленения_WA_4

#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;

vector <int> tin;
vector <int> up;
vector <bool> was;
vector <vector<int>> gr;
vector <bool> cut_p;
int P = 0;
void dfs(int v, int last, int timer) {
    was[v] = true;
    tin[v] = up[v] = timer;

    int child = 0;
    for (int u: gr[v]){

        if (u == last) {

            continue;
        }
        else if (was[u] == true){

            up[v] = min(up[v], tin[u]);
        }
        else if (was[u] == false){
            dfs(u, v, timer + 1);
            up[v] = min(up[v], up[u]);
            if (up[u] >= tin[v] && v != last){
                if (!cut_p[v]) P++;
                cut_p[v] = true;
            }
            child++;
        }
    }
    if (v == last && child > 1) {
        if (!cut_p[v]) P++;
        cut_p[v] = true;
    }

}



int main()
{
    int n, m;
    cin >> n >> m;
    gr.resize(n);
    cut_p.resize(n, false);
    for (int i = 0; i < m; ++i) {
        int a, b;
        cin >> a >> b;
        a--;
        b--;
        gr[a].push_back(b);
        gr[b].push_back(a);
    }
    tin.resize(n, -4);
    up.resize(n, 1e9);
    was.resize(n, false);

    dfs(0, 0, 0);

    cout << P<< '\n';
    for (int i= 0;i<n;++i){
        if (cut_p[i]){
            cout<<i+1<<'\n';
        }
    }
}