code_segments/segment_234.txt

Turtle gives you a string $s$, consisting of lowercase Latin letters.

Turtle considers a pair of integers $(i, j)$ ($1 \le i < j \le n$) to be a pleasant pair if and only if there exists an integer $k$ such that $i \le k < j$ and both of the following two conditions hold:

  * $s_k \ne s_{k + 1}$;    * $s_k \ne s_i$ or $s_{k + 1} \ne s_j$. 

Besides, Turtle considers a pair of integers $(i, j)$ ($1 \le i < j \le n$) to be a good pair if and only if $s_i = s_j$ or $(i, j)$ is a pleasant pair.

Turtle wants to reorder the string $s$ so that the number of good pairs is maximized. Please help him!

Each test contains multiple test cases. The first line contains the number of test cases $t$ ($1 \le t \le 10^4$). The description of the test cases follows.

The first line of each test case contains a single integer $n$ ($2 \le n \le 2 \cdot 10^5$) — the length of the string.

The second line of each test case contains a string $s$ of length $n$, consisting of lowercase Latin letters.

It is guaranteed that the sum of $n$ over all test cases does not exceed $2 \cdot 10^5$.

For each test case, output the string $s$ after reordering so that the number of good pairs is maximized. If there are multiple answers, print any of them.

In the first test case, $(1, 3)$ is a good pair in the reordered string. It can be seen that we can't reorder the string so that the number of good pairs is greater than $1$. bac and cab can also be the answer.

In the second test case, $(1, 2)$, $(1, 4)$, $(1, 5)$, $(2, 4)$, $(2, 5)$, $(3, 5)$ are good pairs in the reordered string. efddd can also be the answer.