CodeForces 615A Bulbs

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 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 42 1 43 1 3 11 2

output

YES

input

3 31 11 21 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.

思路：简单题目，打开的灯标记一下，然后遍历一下就行了

AC代码如下：

#include <iostream>#include <cstring>using namespace std;const int maxn=100+5;int a[maxn];int main(){    int n,m;    while(cin>>n>>m){        memset(a,0,sizeof(a));        for(int i=0;i<n;i++){            int tmp1,tmp;            cin>>tmp1;            while(tmp1--){                cin>>tmp;                if(!a[tmp])                    a[tmp]=1;            }        }        bool ok=true;        int sign=0;        for(int i=1;i<=m;i++){            if(!a[i]){                ok=false;                break;            }            sign++;        }        if(ok && sign==m) cout<<"YES"<<endl;        else cout<<"NO"<<endl;    }    return 0;}