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.util.*;
import java.io.*;
import java.awt.geom.*;
import java.math.*;

public class Main {

	static final Reader in = new Reader();
	static final PrintWriter out = new PrintWriter(System.out,false);
	static boolean debug = false;

	static void solve(){
		int n = in.nextInt();
		int m = in.nextInt();

		DisjointSet ds = new DisjointSet(m);

		boolean[] used = new boolean[m];

		for (int i=0; i<n; i++) {
			int k = in.nextInt();
			int pre = -1;
			for (int j=0; j<k; j++) {
				int l = in.nextInt() - 1;
				used[l] = true;
				if (pre == -1) {
					pre = l;
				} else {
					ds.unite(pre, l);
					pre = l;
				}
			}
		}

		int cnt = 0;
		for (int i=0; i<m; i++) {
			if (!used[i]) {
				cnt++;
			}
		}

		if (ds.size(0) == m - cnt) {
			out.println("YES");
		} else {
			out.println("NO");
		}
	}

	public static void main(String[] args) throws Exception {
		debug = args.length > 0;
		long start = System.nanoTime();

		solve();
		out.flush();

		long end = System.nanoTime();
		dump((end - start) / 1000000 + " ms");
		in.close();
		out.close();
	}

	static void dump(Object... o) { if (debug) System.err.println(Arrays.deepToString(o)); }
}

class DisjointSet {

	private int[] par, cnt;

	public DisjointSet(int n){
		par = new int[n];
		cnt = new int[n];
		for (int i=0; i<n; i++) {
			par[i] = i;
			cnt[i] = 1;
		}
	}

	public int find(int x){
		return par[x] == x ? x : (par[x] = find(par[x]));
	}

	public boolean same(int x, int y){
		return find(x) == find(y);
	}

	public void unite(int x, int y){
		x = find(x); y = find(y);
		if (x == y) return;
		cnt[x] = cnt[y] = cnt[x] + cnt[y];
		par[x] = y;
	}

	public int size(int x) {
		return cnt[find(x)];
	}

	public String toString() {
		return Arrays.toString(par);
	}
}

class Reader {
	private final InputStream in;
	private final byte[] buf = new byte[1024];
	private int ptr = 0;
	private int buflen = 0;

	public Reader() { this(System.in);}
	public Reader(InputStream source) { this.in = source;}

	private boolean hasNextByte() {
		if (ptr < buflen) return true;
		ptr = 0;
		try{
			buflen = in.read(buf);
		}catch (IOException e) {e.printStackTrace();}
		if (buflen <= 0) return false;
		return true;
	}

	private int readByte() { if (hasNextByte()) return buf[ptr++]; else return -1;}

	private boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}

	private void skip() { while(hasNextByte() && !isPrintableChar(buf[ptr])) ptr++;}

	public boolean hasNext() {skip(); return hasNextByte();}

	public String next() {
		if (!hasNext()) throw new NoSuchElementException();
		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while (isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}

	public long nextLong() {
		if (!hasNext()) throw new NoSuchElementException();
		boolean minus = false;
		long num = readByte();

		if(num == '-'){
			num = 0;
			minus = true;
		}else if (num < '0' || '9' < num){
			throw new NumberFormatException();
		}else{
			num -= '0';
		}

		while(true){
			int b = readByte();
			if('0' <= b && b <= '9')
				num = num * 10 + (b - '0');
			else if(b == -1 || !isPrintableChar(b))
				return minus ? -num : num;
			else
				throw new NoSuchElementException();
		}
	}

	public int nextInt() {
		long num = nextLong();
		if (num < Integer.MIN_VALUE || Integer.MAX_VALUE < num)
			throw new NumberFormatException();
		return (int)num;
	}

	public double nextDouble() {
		return Double.parseDouble(next());
	}

	public char nextChar() {
		if (!hasNext()) throw new NoSuchElementException();
		return (char)readByte();
	}

	public String nextLine() {
		while (hasNextByte() && (buf[ptr] == '\n' || buf[ptr] == '\r')) ptr++;
		if (!hasNextByte()) throw new NoSuchElementException();

		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while (b != '\n' && b != '\r' && b != -1) {
			sb.appendCodePoint(b);
			b = readByte();
		}

		return sb.toString();
	}

	public int[] nextIntArray(int n) {
		int[] res = new int[n];
		for (int i=0; i<n; i++) res[i] = nextInt();
		return res;
	}

	public char[] nextCharArray(int n) {
		char[] res = new char[n];
		for (int i=0; i<n; i++) res[i] = nextChar();
		return res;
	}

	public void close() {try{ in.close();}catch(IOException e){ e.printStackTrace();}};
}