First Unique Character in a String

Statement

For a given string of characters, s, your task is to find the first non-repeating character and return its index. Return $-1$ if there’s no unique character in the given string.

Constraints:

• $1 \leq$ s.length $\leq 10^{3}$
• Only lowercase English letters are accepted.
• There are no spaces in the string.

Examples