CF1794A.Prefix and Suffix Array

普及/提高-

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题目描述

Marcos loves strings a lot, so he has a favorite string $s$ consisting of lowercase English letters. For this string, he wrote down all its non-empty prefixes and suffixes (except for $s$ ) on a piece of paper in arbitrary order. You see all these strings and wonder if Marcos' favorite string is a palindrome or not. So, your task is to decide whether $s$ is a palindrome by just looking at the piece of paper.

A string $a$ is a prefix of a string $b$ if $a$ can be obtained from $b$ by deletion of several (possibly, zero or all) characters from the end.

A string $a$ is a suffix of a string $b$ if $a$ can be obtained from $b$ by deletion of several (possibly, zero or all) characters from the beginning.

A palindrome is a string that reads the same backward as forward, for example, strings "gg", "ioi", "abba", "icpci" are palindromes, but strings "codeforces", "abcd", "alt" are not.

输入格式

Each test consists of multiple test cases. The first line contains a single integer $t$ ( $1 \le t \le 120$ ) — the number of test cases. The description of test cases follows.

The first line of each test case contains a single integer $n$ ( $2\le n \le 20$ ) — the length of the string $s$ .

The second line of each test case contains $2n-2$ strings $a_1, a_2, \cdots, a_{2n-2}$ — all non-empty prefixes and suffixes of $s$ , not including itself, in arbitrary order.

It is guaranteed that these strings are all the non-empty prefixes and suffixes of some string consisting of lowercase English letters.

输出格式

For each test case, output "YES" if $s$ is a palindrome, and "NO" otherwise.

You can output the answer in any case (upper or lower). For example, the strings "yEs", "yes", "Yes", and "YES" will be recognized as positive responses.

输入输出样例

输入#1

5
4
bcd cd a d abc ab
3
i io i oi
2
g g
3
t al lt a
4
bba a ab a abb ba

输出#1

NO
YES
YES
NO
YES

说明/提示

In the first test case, $s$ is "abcd". Its prefixes are "a", "ab" and "abc", and its suffixes are "d", "cd" and "bcd". As the string "abcd" is not a palindrome, the answer is NO.

In the second test case, $s$ is "ioi". Its prefixes are "i" and "io", and its suffixes are "i" and "oi". As the string "ioi" is a palindrome, the answer is YES.

In the third test case, $s$ is "gg" which is a palindrome.

In the fourth test case, $s$ is "alt" which is not a palindrome.

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