LeetCode 387. First Unique Character in a String in F#

URL https://leetcode.com/problems/first-unique-character-in-a-string/description/?envType=daily-question&envId=2024-02-05 Code https://github.com/syohex/dotnet-study/blob/master/fsharp/leetcode/challenge/202402/first_unique_character_in_a_string/main...