Codeforces Round #338 (Div. 2) A. Bulbs-优快云博客

本文链接：https://blog.youkuaiyun.com/qq1319479809/article/details/50490104

本文介绍了一道关于通过按钮控制多个灯泡开闭的问题。任务是判断能否通过一系列按钮操作点亮所有灯泡。文章提供了完整的代码实现，并通过样例解释了问题背景及解题思路。

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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 test(s)
 

     input
   
3 4
2 1 4
3 1 3 1
1 2

     output
   
YES

     input
   
3 3
1 1
1 2
1 1

     output
   
NO

Note

In the first sample you can press each button once and turn on all the bulbs. In the 2 sample it is impossible to turn on the 3-rd lamp.

解题报告： Codeforces Round #338 (Div. 2) editorial

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

#include
  
   
#include
   
    
#include
    
     
#include
     
      
#include
      
       
using namespace std;
const int N=1005;
int a[N];
int main()
{
    int i,j;
    int n,m,x,y;
    scanf("%d%d",&n,&m);
    for(i=0; i
       
        m) printf("YES\n"); else printf("NO\n"); return 0; }