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 Python3 (judge verdict: Runtime Error)

from collections import defaultdict
import sys
sys.setrecursionlimit(5*sys.getrecursionlimit())
V, E = map(int, input().split())
G = defaultdict(list)
T = defaultdict(list)
for i in range(E):
    s,t = map(int, input().split())
    G[s].append(t)
    G[t].append(s)

prenum = [float('inf')] * V
lowest = [float('inf')] * V
parent = [None] * V
visited = [False] * V

def dfs(g,s,c=0,p=None):    
    visited[s] = True
    prenum[s] = c
    lowest[s] = c
    c+=1    
    for v in g[s]:
        if not visited[v]:
            parent[v] = s
            T[v].append(s)
            T[s].append(v)
            dfs(g,v,c,s)
            lowest[s] = min( lowest[s], lowest[v] )
        elif v != p:
            lowest[s] = min( lowest[s], prenum[v] )

dfs(G,0)
k = []
if len(T[0]) > 1: k.append(0)
for u in range(V):
    p = parent[u]
    if p is None or p == 0: continue
    if prenum[p] <= lowest[u]: k.append(p)
for i in sorted(set(k)):
    print(i)