Problem:
Articulation Points

Find articulation points of a given undirected graph G(V, E).

A vertex in an undirected graph is an articulation point (or cut vertex) iff removing it disconnects the graph.

Input

|V| |E|
s0 t0
s1 t1
:
s|E|-1 t|E|-1

, where |V| is the number of vertices and |E| is the number of edges in the graph. The graph vertices are named with the numbers 0, 1,..., |V|-1 respectively.

si and ti represent source and target verticess of i-th edge (undirected).

Output

A list of articulation points of the graph G ordered by name.

Constraints

1 ≤ |V| ≤ 100,000

0 ≤ |E| ≤ 100,000

The graph is connected

There are no parallel edges

There are no self-loops

Sample Input 1

4 4
0 1
0 2
1 2
2 3

Sample Output 1

2

Sample Input 2

5 4
0 1
1 2
2 3
3 4

Sample Output 2

1
2
3

Solution in C++14 (judge verdict: Accepted)

#include <bits/stdc++.h>
#define pb push_back
using namespace std;

const int mx = 100005;

int dtime = 0;
int n, m, par[mx], low[mx], start[mx];
vector<int> adj[mx], child[mx];
bool vis[mx];
set<int> art;

void dfs(int n, int p = -1) {
  //printf("DFS %d from %d\n", n, p);
  vis[n] = true;
  par[n] = p;
  child[p].pb(n);
  start[n] = dtime++;
  low[n] = start[n];
  
  for (int h : adj[n]) {
    if (!vis[h]) {
      dfs(h, n);
      // printf("Low[%d] = min(%d, %d) = %d\n", n, low[n], low[h], min(low[n], low[h]));
      low[n] = min(low[h], low[n]);
      if ((n == 0 && child[0].size() > 1) || (n != 0 && low[h] >= start[n])) {
	art.insert(n);
      }
    } else if (h != p) {
      low[n] = min(low[n], start[h]);
    }
  }
}

int main() {
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int u, v; cin >> u >> v;
    adj[u].pb(v); adj[v].pb(u);
  }
  dfs(0);
  for (int h : art) cout << h << endl;
}