URL

https://leetcode.com/problems/sort-characters-by-frequency/description/

Code

https://github.com/syohex/dotnet-study/blob/master/fsharp/leetcode/challenge/202402/sort_characters_by_frequency/main.fsx

let frequencySort (s: string) : string =
    s
    |> Seq.fold
        (fun acc c ->
            match Map.tryFind c acc with
            | Some(v) -> Map.add c (v + 1) acc
            | None -> Map.add c 1 acc)
        Map.empty
    |> Map.toList
    |> List.sortWith (fun (c1, n1) (c2, n2) -> if n1 = n2 then compare c1 c2 else compare n2 n1)
    |> List.fold (fun acc (c, v) -> seq { 1..v } |> Seq.fold (fun acc _ -> acc + string c) acc) ""