First non-repeating character

Two-pass ordered scan.

dict strings counter

Implement `first_unique(s: str) -> int`.

Return the index of the first non-repeating character, or -1 if none.

Constraints

0 ≤ len(s) ≤ 10^5; only lowercase letters.

Example

>>> first_unique("loveleetcode")
2

12 points ~12 min

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Hints

Count all chars, then scan for first with count == 1.

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