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# (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using static System.Console;
using static System.Convert;
using static System.Math;
//using Debug;
//using static System.Globalization.CultureInfo;
//using Edge = Pair<long, int>;
using System.Text;
class Program
{
    static void Main(string[] args)
    {
        var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
        Console.SetOut(sw);
        Solve();
        Console.Out.Flush();
        //WriteLine(Solve());
    }
    static void Solve()
    {
        var ve = Input.ar;
        var adj = Enumerable.Repeat(0, ve[0]).Select(_ => new List<int>()).ToArray();
        while (ve[1]-- > 0)
        {
            var st = Input.ar;
            adj[st[0]].Add(st[1]);
            adj[st[1]].Add(st[0]);
        }
        var l = LowLink.Articulation(adj);
        if(l.Count!=0)
        WriteLine(string.Join("\n", l.OrderBy(v=>v)));
    }
}

public class LowLink
{
    private static List<int> arti;
    private static int[] ord, low;
    private static List<Pair<int, int>> bridge;
    private static bool[] th;
    private static IList<IEnumerable<int>> adj;
    public static List<int> Articulation(IList<IEnumerable<int>> edge)
    {
        adj = edge;
        arti = new List<int>();
        ord = new int[edge.Count];
        low = new int[edge.Count];
        bridge = new List<Pair<int, int>>();
        th = new bool[edge.Count];
        var ct = 0;
        for (var i = 0; i < edge.Count; i++)
            if (!th[i]) ct = dfs(i, ct, -1);
        return arti;
    }
    public static List<Pair<int,int>> Bridge(IList<IEnumerable<int>> edge)
    {
        Articulation(edge);
        return bridge;
    }
    private static int dfs(int index,int ct,int par)
    {
        th[index] = true;
        ord[index] = ct;
        low[index] = ct++;
        var isArti = false;
        var c = 0;
        foreach (var ad in adj[index])
            if(!th[ad])
            {
                c++;
                ct = dfs(ad, ct, index);
                low[index] = Min(low[index], low[ad]);
                isArti |= par != -1 && low[ad] >= ord[index];
                if (ord[index] < low[ad])
                    bridge.Add(new Pair<int, int>(index, ad));   
            }
            else if (ad != par)
                low[index] = Min(low[index], ord[ad]);
        isArti |= par == -1 && c > 1;
        if (isArti) arti.Add(index);
        return ct;
    }
}

public class Input
{
    public static string read => ReadLine().Trim();
    public static int[] ar => read.Split(' ').Select(int.Parse).ToArray();
    public static int num => ToInt32(read);
    public static long[] arL => read.Split(' ').Select(long.Parse).ToArray();
    public static long numL => ToInt64(read);
    public static char[][] gred(int h)
        => Enumerable.Repeat(0, h).Select(_ => read.ToCharArray()).ToArray();
    public static int[] ar1D(int n)
        => Enumerable.Repeat(0, n).Select(_ => num).ToArray();
    public static long[] arL1D(int n)
        => Enumerable.Repeat(0, n).Select(_ => numL).ToArray();
    public static string[] strs(int n)
        => Enumerable.Repeat(0, n).Select(_ => read).ToArray();
    public static int[][] ar2D(int n)
        => Enumerable.Repeat(0, n).Select(_ => ar).ToArray();
    public static long[][] arL2D(int n)
        => Enumerable.Repeat(0, n).Select(_ => arL).ToArray();
    public static T getValue<T>(string g)
    {
        var t = typeof(T);
        if (t == typeof(int))
            return (T)(object)int.Parse(g);
        if (t == typeof(long))
            return (T)(object)long.Parse(g);
        if (t == typeof(string))
            return (T)(object)g;
        if (t == typeof(char))
            return (T)(object)char.Parse(g);
        if (t == typeof(double))
            return (T)(object)double.Parse(g);
        if (t == typeof(bool))
            return (T)(object)bool.Parse(g);
        return default(T);
    }
    public static string[] Make<T1, T2>(out T1 v1, out T2 v2)
    {
        var r = read.Split(' ');
        v1 = getValue<T1>(r[0]);
        v2 = getValue<T2>(r[1]);
        return r;
    }
    public static string[] Make<T1, T2, T3>(out T1 v1, out T2 v2, out T3 v3)
    {
        var r = Make(out v1, out v2);
        v3 = getValue<T3>(r[2]);
        return r;
    }
    public static string[] Make<T1,T2,T3,T4>(out T1 v1,out T2 v2,out T3 v3,out T4 v4)
    {
        var r = Make(out v1, out v2, out v3);
        v4 = getValue<T4>(r[3]);
        return r;
    }
    public const long Inf = (long)1e18;
    public const double eps = 1e-6;
    public const string Alfa = "abcdefghijklmnopqrstuvwxyz";
    public const int MOD = 1000000007;
}

public class Pair<T1, T2> : IComparable<Pair<T1, T2>>
{
    public T1 v1 { get; set; }
    public T2 v2 { get; set; }
    public Pair() : this(default(T1), default(T2)) { }
    public Pair(T1 v1, T2 v2)
    { this.v1 = v1;this.v2 = v2; }

    public int CompareTo(Pair<T1, T2> p)
    {
        var c = Comparer<T1>.Default.Compare(v1, p.v1);
        if (c == 0)
            c = Comparer<T2>.Default.Compare(v2, p.v2);
        return c;
    }
    public override string ToString()
        => $"{v1.ToString()} {v2.ToString()}";
}