articulation_points.cpp

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;

template <class T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

#define int long long int
#define pb push_back
#define pi pair<int, int>
#define pii pair<int, pi>
#define fir first
#define sec second
#define MAXN 400005
#define mod 1000000007

int n, m, timer;
vector<int> adj[MAXN];
bool is_cutpoint[MAXN];
int tin[MAXN];
int low[MAXN];
bool vis[MAXN];

void dfs(int v, int p)
{
  vis[v] = true;
  tin[v] = timer, low[v] = timer++;
  int childs = 0;
  for (auto const &u : adj[v])
  {
    if (u == p)
      continue;
    if (vis[u])
    {
      low[v] = min(low[v], tin[u]);
    }
    else
    {
      dfs(u, v);
      low[v] = min(low[v], low[u]);
      if (low[u] >= tin[v] && p != -1)
        is_cutpoint[v] = true;
      childs++;
    }
  }
  if (p == -1 && childs > 1)
    is_cutpoint[v] = true;
}
signed main()
{
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> n >> m;
  for (int i = 0; i < m; i++)
  {
    int a, b;
    cin >> a >> b;
    a--, b--;
    adj[a].pb(b);
    adj[b].pb(a);
  }
  memset(tin, -1, sizeof(tin));
  memset(low, -1, sizeof(low));
  for (int i = 0; i < n; i++)
  {
    if (!vis[i])
      dfs(i, -1);
  }
  return 0;
}