First Unique Character Index

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Your question is First Unique Character Index. Start with the requirements on the right.

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Problem

At Spotify, you are given a lowercase string s and need to find the index of the first character that appears exactly once. If no such character exists, return -1.

Formal Specification

Input: A string s containing only lowercase English letters.
Output: An integer representing the index of the first non-repeating character, or -1 if every character repeats.

Constraints

1 <= len(s) <= 10^5
s contains only lowercase English letters

Function Signature

def first_unique_char(s):

Your solutionPython 3

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