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.Generic;
using System.Text;

namespace AtTest._400Problems_remain_
{
    class CF2016Final_C
    {
        static void Main(string[] args)
        {
            Method(args);
            Console.ReadLine();
        }

        static void Method(string[] args)
        {
            int[] nm = ReadInts();
            int n = nm[0];
            int m = nm[1];
            var edges = new Queue<int>[m];
            for(int i = 0; i < m; i++)
            {
                edges[i] = new Queue<int>();
            }
            for (int i = 0; i < n; i++)
            {
                int[] kls = ReadInts();
                for (int j = 0; j < kls[0]; j++)
                {
                    edges[kls[j + 1] - 1].Enqueue(i);
                }
            }
            var parents = new int[n];
            var ranks = new int[n];
            for (int i = 0; i < n; i++) parents[i] = i;
            for (int i = 0; i < m; i++)
            {
                if (edges[i].Count <= 1) continue;
                int parent = edges[i].Dequeue();
                while (edges[i].Count > 0)
                {
                    int index = edges[i].Dequeue();
                    Unite(ref parents, ref ranks, parent, index);
                }
            }
            int cnt = 0;
            for (int i = 0; i < n; i++)
            {
                //Console.WriteLine(parents[i]);
                if (parents[i] != i) cnt++;
            }
            Console.WriteLine(cnt == n - 1 ? "YES" : "NO");
        }

        static int Root(ref int[] tree, int x)
        {
            int rx = x;
            while (tree[rx] != rx)
            {
                rx = tree[rx];
            }
            tree[x] = rx;
            return rx;
        }

        static bool IsSame(ref int[] tree, int x, int y)
        {
            return Root(ref tree, x)
                == Root(ref tree, y);
        }

        static void Unite(ref int[] tree, ref int[] rank,
            int x, int y)
        {
            int rx = Root(ref tree, x);
            int ry = Root(ref tree, y);
            if (rx == ry) return;
            if (rank[rx] < rank[ry])
            {
                int temp = rx;
                rx = ry;
                ry = temp;
            }
            if (rank[rx] == rank[ry])
            {
                rank[rx]++;
            }
            tree[ry] = rx;
        }

        private static string Read() { return Console.ReadLine(); }
        private static int ReadInt() { return int.Parse(Read()); }
        private static long ReadLong() { return long.Parse(Read()); }
        private static double ReadDouble() { return double.Parse(Read()); }
        private static int[] ReadInts() { return Array.ConvertAll(Read().Split(), int.Parse); }
        private static long[] ReadLongs() { return Array.ConvertAll(Read().Split(), long.Parse); }
        private static double[] ReadDoubles() { return Array.ConvertAll(Read().Split(), double.Parse); }
    }
}