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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.io.*;
import java.lang.*;
import java.util.*;

public class Main {

	static int count = 0;
	static boolean[] m;
	static Map<Integer, List<Integer>> spoken;
	static int[][] L;

	public static void main(String[] args) throws IOException {
		BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
		int N = Integer.parseInt(reader.readLine().split("\\s")[0]);
		L = new int[N][];
		m = new boolean[N];
		spoken = new HashMap();
		for (int j = 0; j < N; j++) {
			String[] raw = reader.readLine().split("\\s");
			L[j] = new int[Integer.parseInt(raw[0])];
			for (int k = 0; k < L[j].length; k++) {
				L[j][k] = Integer.parseInt(raw[k+1]);
				if (!spoken.containsKey(L[j][k]))
					spoken.put(L[j][k], new ArrayList());
				spoken.get(L[j][k]).add(j);
			}
		}
		dfs(N, 0);
		System.out.println(count == N ? "YES" : "NO");
	}

	static void dfs(int N, int current) {
		count++;
		if (count == N) return;
		m[current] = true;
		for (int k = 0; k < L[current].length; k++) {
			int lang = L[current][k];
			for (int v: spoken.get(lang))
				if (!m[v])
					dfs(N,v);
		}
	}
	
}