Problem:
Score : 400 points

Problem Statement

On a planet far, far away, M languages are spoken. They are conveniently numbered 1 through M.

For CODE FESTIVAL 20XX held on this planet, N participants gathered from all over the planet.

The i-th (1≦i≦N) participant can speak K_i languages numbered L_{i,1}, L_{i,2}, ..., L_{i,{}K_i}.

Two participants A and B can communicate with each other if and only if one of the following conditions is satisfied:

There exists a language that both A and B can speak.

There exists a participant X that both A and B can communicate with.

Determine whether all N participants can communicate with all other participants.

Constraints

2≦N≦10^5

1≦M≦10^5

1≦K_i≦M

(The sum of all K_i)≦10^5

1≦L_{i,j}≦M

L_{i,1}, L_{i,2}, ..., L_{i,{}K_i} are pairwise distinct.

Partial Score

200 points will be awarded for passing the test set satisfying the following: N≦1000, M≦1000 and (The sum of all K_i)≦1000.

Additional 200 points will be awarded for passing the test set without additional constraints.

Input

The input is given from Standard Input in the following format:

N M
K_1 L_{1,1} L_{1,2} ... L_{1,{}K_1}
K_2 L_{2,1} L_{2,2} ... L_{2,{}K_2}
:
K_N L_{N,1} L_{N,2} ... L_{N,{}K_N}

Output

If all N participants can communicate with all other participants, print YES. Otherwise, print NO.

Sample Input 1

4 6
3 1 2 3
2 4 2
2 4 6
1 6

Sample Output 1

YES

Any two participants can communicate with each other, as follows:

Participants 1 and 2: both can speak language 2.

Participants 2 and 3: both can speak language 4.

Participants 1 and 3: both can communicate with participant 2.

Participants 3 and 4: both can speak language 6.

Participants 2 and 4: both can communicate with participant 3.

Participants 1 and 4: both can communicate with participant 2.

Note that there can be languages spoken by no participant.

Sample Input 2

4 4
2 1 2
2 1 2
1 3
2 4 3

Sample Output 2

NO

For example, participants 1 and 3 cannot communicate with each other.

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;

class TEST{
	static void Main(){
		Sol mySol =new Sol();
		mySol.Solve();
	}
}

class Sol{
	public void Solve(){
		
		var UF = new UnionFind(N);
		Dictionary<int,int> D = new Dictionary<int,int>();
		for(int i=0;i<N;i++){
			for(int j=0;j<K[i];j++){
				if(D.ContainsKey(L[i][j]) == false) D.Add(L[i][j],i);
				UF.Unite(D[L[i][j]],i);
			}
		}
		
		Console.WriteLine(UF.Compo == 1 ? "YES" : "NO");
		
		
		
		
	}
	int N,M;
	int[] K;
	int[][] L;
	
	public Sol(){
		var d = ria();
		N = d[0]; M = d[1];
		K = new int[N];
		L = new int[N][];
		for(int i=0;i<N;i++){
			d = ria();
			K[i] = d[0];
			L[i] = new int[K[i]];
			for(int j=0;j<L[i].Length;j++) L[i][j] = d[j+1];
		}
		
		
		
	}

	static String rs(){return Console.ReadLine();}
	static int ri(){return int.Parse(Console.ReadLine());}
	static long rl(){return long.Parse(Console.ReadLine());}
	static double rd(){return double.Parse(Console.ReadLine());}
	static String[] rsa(char sep=' '){return Console.ReadLine().Split(sep);}
	static int[] ria(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>int.Parse(e));}
	static long[] rla(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>long.Parse(e));}
	static double[] rda(char sep=' '){return Array.ConvertAll(Console.ReadLine().Split(sep),e=>double.Parse(e));}
}
class UnionFind{
	
	int[] parent;
	int[] mem;
	int compo;
	int N;
	public UnionFind(int n_){
		Initialize(n_);
	}
	
	public void Initialize(int n_){
		N=n_;
		parent=new int[N];
		mem=new int[N];
		for(int i=0;i<N;i++){
			parent[i]=i;
			mem[i]=1;
		}
		compo=N;
	}
	
	public int Parent(int a){
		if(parent[a]==a)return a;
		return parent[a]=Parent(parent[a]);
	}
	
	public bool IsUnited(int a,int b){
		return Parent(a)==Parent(b);
	}
	
	public void Unite(int a,int b){
		a=Parent(a);b=Parent(b);//Parent()を呼ぶことでa以上のノードは全てparentがrootになる
		if(a==b)return;
		parent[a]=b;
		mem[b]+=mem[a];
		compo-=1;
	}
	
	public bool IsRoot(int x){
		return x==parent[x];
	}
	public int MemCnt(int x){
		return mem[Parent(x)];
	}
	
	public void Dump(){
		for(int i=0;i<parent.Length;i++){
			Console.Write(i==0?"{0}":" {0}",parent[i]);
		}
		Console.WriteLine("");
	}
	
	public int Compo{
		get{
			return compo;
		}
	}
	
}