Modify the String

Problem Overview

• Given a string input_str of length n, repeatedly delete one occurrence of any duplicate character until all characters are distinct, then return the lexicographically maximum string.
• Input: string input_str; Output: a string with unique characters that is lexicographically maximal.
• Domain: string processing and text normalization, focusing on deduplication with ordering.
• Often used in coding interview prep, this interview question is a string manipulation problem.