CodeForces 615A Bulbs （开灯问题）

A. Bulbs

time limit per test
1 second

memory limit per test
256 megabytes

input
standard input

output
standard output

Vasya wants to turn on Christmas lights consisting of m bulbs. Initially, all bulbs are turned off. There aren 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 andm (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 thei-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".

Examples

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.

参考题意：

就是好多灯和一些开关，问你能不能把所有的灯打开。

参考代码：

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>
#include<algorithm>
#define MYDD 108

using namespace std;

int main() {//英语不好的同学，有哪些细节被忽略
int n,m,k,t;
int wqs[MYDD];//灯泡的状态 -1 关；1 开
int flag;
while(scanf("%d%d",&n,&m)!=EOF) {//  n 个开关，m 个灯
flag=1;
for(int j=1; j<=m; j++)
wqs[j]=-1;//初始化灯泡:全部关闭

for(int j=0; j<n; j++) {
scanf("%d",&t);
for(int i=0; i<t; i++) {
scanf("%d",&k);
if(wqs[k]==-1)//已经打开灯的状态不变
wqs[k]=1;//打开灯
}
}

for(int j=1; j<=m; j++)
if(wqs[j]==-1) {
flag=0;
break;
}

if(flag)
puts("YES");
else
puts("NO");
}
return 0;
}

/*

*/