【codeforces】Bulbs

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本文介绍了一个关于通过按按钮来点亮所有圣诞灯泡的问题，并提供了一段C语言代码实现。问题中涉及n个按钮和m个初始关闭的灯泡，每个按钮可以开启一组特定的灯泡。目标是判断是否能通过按下某些按钮使所有灯泡都亮起。

Bulbs

Time Limit:1000MS Memory Limit:262144KB 64bit IO Format:%I64d & %I64u

Submit Status

Description

Vasya wants to turn on Christmas lights consisting of m bulbs. Initially, all bulbs are turned off. There are n buttons, each of them is connected to some set of bulbs. Vasya can press any of these buttons. When the button is pressed, it turns on all the bulbs it's connected to. Can Vasya light up all the bulbs?

If Vasya presses the button such that some bulbs connected to it are already turned on, they do not change their state, i.e. remain turned on.

Input

The first line of the input contains integers n and m (1 ≤ n, m ≤ 100) — the number of buttons and the number of bulbs respectively.

Each of the next n lines contains x_i (0 ≤ x_i ≤ m) — the number of bulbs that are turned on by the i-th button, and then x_i numbers y_ij (1 ≤ y_ij ≤ m) — the numbers of these bulbs.

Output

If it's possible to turn on all m bulbs print "YES", otherwise print "NO".

Sample Input

Input

Output

YES

Input

Output

NO

     
      
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       #include<stdio.h>
int main()
{
	int p[100];
	int n,m;
	while(scanf("%d%d",&n,&m)!=EOF)
	{
	        for(int i=1;i<=m;i++)
			p[i]=0;//所有灯泡为关闭状态
		for(int i=1;i<=n;i++)
		{
			int t,j;
			scanf("%d",&t);
			while(t--)
			{
				scanf("%d",&j);
				p[j]=1;//开灯
			}	
		}
		int l=1;
	for(int i=1;i<=m;i++)
	{
		if(p[i]==0)//判断是否有的灯泡没打开
	  {
		l=0;
		break;}
	}	
	if(l==1)
	printf("YES\n");
	else
	printf("NO\n");
	}
	return 0;
}