A12606 | Pairs
时间限制1s
内存限制256MB
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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 $y$ .
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.
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
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 $y=2$ .
In the second example, you can choose $x=2$ and $y=4$ .
In the third example, you can choose $x=1$ and $y=2$ .
C++ 编辑器
输入
输出
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评测结果：Accepted