First Unique Character in a String

Easy

Given a string s, return the index of the first non-repeating character. If none exists, return -1.

Example 1

Input:  s = "leetcode"
Output: 0

Example 2

Input:  s = "loveleetcode"
Output: 2

Example 3

Input:  s = "aabb"
Output: -1

Constraints

• 1 <= s.length <= 10^5
• s consists of lowercase English letters.