String Non-Repeating Character | Dataford Interview Questions

Write a program to find the first non-repeating character in a given string and analyze its time complexity.

Implement def first_non_repeating_char(s):. Return the first character whose frequency is exactly one, or None if no such character exists. Treat uppercase and lowercase characters as distinct, and count spaces and punctuation as ordinary characters.

Input and Output

Input: a string s with length from 0 to 100,000.
Output: a single-character string or None.

Constraints

0 <= len(s) <= 100000
The string may contain letters, digits, spaces, punctuation, and Unicode characters
Character comparisons are case-sensitive

Function Signature

def first_non_repeating_char(s):

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