CF1169B.Pairs

普及/提高-

通过率：0%

AC君温馨提醒

该题目为【codeforces】题库的题目，您提交的代码将被提交至codeforces进行远程评测，并由ACGO抓取测评结果后进行展示。由于远程测评的测评机由其他平台提供，我们无法保证该服务的稳定性，若提交后无反应，请等待一段时间后再进行重试。

题目描述

Toad Ivan has $m$ pairs of integers, each integer is between $1$ and $n$ , inclusive. The pairs are $(a_1, b_1), (a_2, b_2), \ldots, (a_m, b_m)$ .

He asks you to check if there exist two integers $x$ and $y$ ( $1 \leq x < y \leq n$ ) such that in each given pair at least one integer is equal to $x$ or $y$ .

输入格式

The first line contains two space-separated integers $n$ and $m$ ( $2 \leq n \leq 300\,000$ , $1 \leq m \leq 300\,000$ ) — the upper bound on the values of integers in the pairs, and the number of given pairs.

The next $m$ lines contain two integers each, the $i$ -th of them contains two space-separated integers $a_i$ and $b_i$ ( $1 \leq a_i, b_i \leq n, a_i \neq b_i$ ) — the integers in the $i$ -th pair.

输出格式

Output "YES" if there exist two integers $x$ and $y$ ( $1 \leq x < y \leq n$ ) such that in each given pair at least one integer is equal to $x$ or $y$ . Otherwise, print "NO". You can print each letter in any case (upper or lower).

输入输出样例

输入#1
```
4 6
1 2
1 3
1 4
2 3
2 4
3 4
```
输出#1
```
NO
```
输入#2
```
5 4
1 2
2 3
3 4
4 5
```
输出#2
```
YES
```
输入#3
```
300000 5
1 2
1 2
1 2
1 2
1 2
```
输出#3
```
YES
```

说明/提示

In the first example, you can't choose any $x$ , $y$ because for each such pair you can find a given pair where both numbers are different from chosen integers.

In the second example, you can choose $x=2$ and $y=4$ .

In the third example, you can choose $x=1$ and $y=2$ .

首页