URL

leetcode.com/problems/sort-characters-by-fr..

Code

github.com/syohex/dotnet-study/blob/master/..

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, n) ->
            seq { 1..n }
            |> Seq.fold (fun acc2 _ -> c :: acc2) acc)
        []
    |> List.rev
    |> System.String.Concat