Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

 

Example 1:

Input: s = "coderplayground"

Output: 0

Explanation:

The character 'c' at index 0 is the first character that does not occur at any other index.

Example 2:

Input: s = "lovecoderplayground"

Output: 2

Example 3:

Input: s = "aabb"

Output: -1

 

Constraints:

• 1 <= s.length <= 105
• s consists of only lowercase English letters.