write a go solution for Description:
Polycarp has a string s, which consists of lowercase Latin letters. He encodes this string using the following algorithm:

- first, he constructs a new auxiliary string r, which consists of all distinct letters of the string s, written in alphabetical order;
- then the encoding happens as follows: each character in the string s is replaced by its symmetric character from the string r (the first character of the string r will be replaced by the last, the second by the second from the end, and so on).

For example, encoding the string s="codeforces" happens as follows:

- the string r is obtained as "cdefors";
- the first character s_1='c' is replaced by 's';
- the second character s_2='o' is replaced by 'e';
- the third character s_3='d' is replaced by 'r';
- ...
- the last character s_10='s' is replaced by 'c'.

The string r and replacements for s="codeforces".

Thus, the result of encoding the string s="codeforces" is the string "serofedsoc".

Write a program that performs decoding — that is, restores the original string s from the encoding result.

Input Format:
The first line contains a single integer t (1<=t<=10^4) — the number of test cases.

The first line of each test case contains a single integer n (1<=n<=2*10^5) — the length of the string b.

The second line of each test case contains a string b of length n, consisting of lowercase Latin letters — the result of encoding the original string s.

It is guaranteed that the sum of the values of n over all test cases in the test does not exceed 2*10^5.

Output Format:
For each test case, output the string s from which the encoding result b was obtained.

Note:
None. Output only the code with no comments, explanation, or additional text.