Counting Sort Question

Given a string S consisting of lowercase latin letters, arrange all its letters in lexographical order using Counting Sort.

Input:
The first line of the input contains T denoting number of testcases.Then T test cases follow. Each testcase contains positive integer N denoting the length of string.The last line of input contains the string S.

Output:
For each testcase, in a new line, output the sorted string.

Your Task:
This is a function problem. You only need to complete the function countSort() that takes char array as parameter and return the sorted char array. The printing is done by driver code.

Constraints:
1 <= T <= 105
1 <= N <= 105

Example:
Input:
2
5
edsab
13
geeksforgeeks
Output:
abdes
eeeefggkkorss

Explanation:
Testcase 1: In lexicographical order , string will be abdes.
Testcase 2: In lexicographical order , string will be eeeefggkkorss.