Find First Unique Character in a String

You are given a string S of length N. Your task is to find the index (considering 1-based indexing) of the first unique character in the string. If there are no unique characters, return -1.

Example:

Input:

 T = 2 
 N = 5 
 S = "hello" 
 N = 4 
 S = "aabb" 

Output:

 1 
 -1 

Explanation:

The first unique character in "hello" is 'h', which is at index 1. The string "aabb" has no unique characters.

Constraints:

• 1 ≤ T ≤ 100
• 1 ≤ N ≤ 10^4

Note:

A unique character in a string is one that appears only once.