a_and_b.cpp

#include <bits/stdc++.h>
#define f first
#define s second
#define pb push_back
#define mp make_pair
#define ll long long

#define IOS ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);

using namespace std;
const int INF = 1e9 + 1;
const int MAXN = 2e5 + 10;
int tin[MAXN], a[2 * MAXN], tout[MAXN], ans[MAXN], col[MAXN], cnt[MAXN], cntCnt[MAXN];
int n, m;
pair <pair <int, int>, pair <int, pair <int, int> > > b[MAXN];
int timer = 0;
bool was[MAXN];
vector <int> g[MAXN];

void dfs(int v, int pr = -1){
    was[v] = 1;
    tin[v] = ++timer;
    fup[v] = tin[v];
    for (int to : g[v]){
        if (!was[to]){
            dfs(to, v);
            if (tin[v] > fup[to]){
                is_bridge(v, to);
            }
            fup[v] = min(fup[v], fup[to]);
        }
        else if (to != pr){
            fup[v] = min(fup[v], tin[to]);
        }
    }
}


void dfs(int v, int pr = -1){
    was[v] = 1;
    tin[v] = ++timer;
    fup[v] = tin[v];
    int child = 0;
    for (int to : g[v]){
        if (!was[to]){
            child++;
            dfs(to, v);
            if (tin[v] >= fup[to] && pr != -1){
                is_point(v);
            }
            fup[v] = min(fup[v], fup[to]);
        }
        else if (to != pr){
            fup[v] = min(fup[v], tin[to]);
        }
    }
    if (pr == -1 && child > 1){
        is_point(v);
    }
}
void solve(){
    int n, m;
    cin >> n >> m;

    for (int i = 1; i <= m; i++){
        int x, y;
        cin >> x >> y;
        g[x].pb(y);
        g[y].pb(x);
    }

    for (int i = 1; i <= n; i++){
        if (!was[i]){
            dfs(i, -1);
        }
    }
}
int main() {
    IOS;
    //freopen("rmq.in", "r", stdin);
    //freopen("rmq.out", "w", stdout);
    int t = 1;
   // cin >> t;
    while(t--){
        solve();
    }
    return 0;
}