First Non-Repeating Character

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Your question is First Non-Repeating Character. Start with the requirements on the right.

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Problem

Given a string s, return the first character that appears exactly once when scanning from left to right. If no such character exists, return an empty string "". Write a Python function that solves this efficiently and be prepared to analyze its time complexity.

Constraints

0 <= len(s) <= 10^5
s consists of printable characters
Return an empty string if no non-repeating character exists

Function Signature

def first_non_repeating_char(s):

Your solutionPython 3

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