Most Frequent Character | Dataford Interview Questions

Quantiphi's language-processing pipelines may need a quick summary of incoming text. Write a function that returns the character occurring most frequently in a non-empty string.

Character comparison is case-sensitive, and every character counts, including spaces, punctuation, and digits. If multiple characters have the same highest frequency, return the one that appears first in the original string.

Formal Specification

Input: A non-empty Python string s.
Output: A one-character string containing the most frequent character in s.
The input may contain letters, digits, whitespace, punctuation, or Unicode characters.

Constraints

1 <= len(s) <= 10^5
The input may contain letters, digits, whitespace, punctuation, or Unicode characters.
Character matching is case-sensitive.
If frequencies tie, return the character with the earliest index in the string.

Function Signature

def most_frequent_char(s):

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