Longest Sub-string with at most K Distinct Characters

You are given string S of length N, and an integer K. Your task is to find the length of the longest substring that contains at most K distinct characters.

Input Format:

The first line contains an Integer 'T' which denotes the number of test cases/queries to be run. 
Then the test cases follow. 

The first line of input for each test case/query contains an integer K.

The second line of input for each test case/query contains a string S.

Output Format:

For each test case, print the length of the longest substring that contains at most K distinct characters.

Output for every test case will be printed in a separate line.

Note:

You do not need to print anything, it has already been taken care of. Just implement the function.

Constraints:

1 <= T <= 10
1 <= K <= 26
1 <= N <= 10^4

Time Limit: 1sec