Codeforces Round #338 (Div. 2) A. Bulbs 水题

A. Bulbs

题目连接：

http://www.codeforces.com/contest/615/problem/A

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 xi (0 ≤ xi ≤ m) — the number of bulbs that are turned on by the i-th button, and then xi numbers yij (1 ≤ yij ≤ m) — the numbers of these bulbs.

Output

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

Sample Input

3 4

2 1 4

3 1 3 1

1 2

Sample Output

YES

Hint

题意

给你n个开关，一共有m个灯

每个开关控制ai个灯，只要按下这个开关，那么ai个灯都会亮

问你是否可以使得所有m个灯都能够亮起来

题解：

直接把所有的灯都扫一遍，然后看看是不是都出现过就好了

代码

#include<bits/stdc++.h>
using namespace std;

int a[500];
int main()
{
    int n,m;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++)
    {
        int x;scanf("%d",&x);
        for(int j=1;j<=x;j++)
        {
            int y;scanf("%d",&y);
            a[y]=1;
        }
    }
    int flag = 0;
    for(int i=1;i<=m;i++)
    {
        if(a[i]==0)
            flag = 1;
    }
    if(flag)return puts("NO");
    else puts("YES");
}