3039. Apply Operations to Make String Empty

You are given a string s. Consider performing the following operation until s becomes empty: - For every alphabet character from 'a' to 'z', remove the first occurrence of that character in s (if it exists). For example, let initially s = "aabcbbca". We do the following operations: - Remove the underlined characters s = "aabcbbca". The resulting string is s = "abbca". - Remove the underlined