Kata.elm

module Kata exposing (fromNb2Str)


fromNb2Str n modsys =
    let
        gcd : Int -> Int -> Int
        gcd a b =
            if b == 0 then
                a

            else
                gcd b (modBy b a)

        lcm : Int -> Int -> Int
        lcm a b =
            (a * b) // gcd a b

        isPairwiseCoprime : Int -> List Int -> Bool
        isPairwiseCoprime prod xs =
            List.foldl (\acc x -> lcm x acc) 1 xs == prod

        product : Int
        product =
            List.product modsys
    in
    if isPairwiseCoprime product modsys && product > n then
        "-" ++ (modsys |> List.map (\m -> modBy m n |> String.fromInt) |> String.join "--") ++ "-"

    else
        "Not applicable"