First Unique Character in a String

lcpy gen -n 387   # by problem number
lcpy gen -s first_unique_character_in_a_string   # by problem name

Input: s = "leetcode"
Output: 0
Explanation: The character 'l' at index 0 is the first character that does not occur at any other index.

Input: s = "loveleetcode"
Output: 2

Input: s = "aabb"
Output: -1

from collections import Counter


class Solution:
    # Time: O(n)
    # Space: O(1)
    def first_uniq_char(self, s: str) -> int:
        counts = Counter(s)
        for i, ch in enumerate(s):
            if counts[ch] == 1:
                return i
        return -1