open System

let TABLE = [|
    [|0; 3; 1; 7; 5; 9; 8; 6; 4; 2|];
    [|7; 0; 9; 2; 1; 5; 4; 8; 6; 3|];
    [|4; 2; 0; 6; 8; 7; 1; 3; 5; 9|];
    [|1; 7; 5; 0; 9; 8; 3; 4; 2; 6|];
    [|6; 1; 2; 3; 0; 4; 5; 9; 7; 8|];
    [|3; 6; 7; 4; 2; 0; 9; 5; 8; 1|];
    [|5; 8; 6; 9; 7; 2; 0; 1; 3; 4|];
    [|8; 9; 4; 5; 3; 6; 2; 0; 1; 7|];
    [|9; 4; 3; 8; 6; 1; 7; 2; 0; 5|];
    [|2; 5; 8; 1; 4; 3; 6; 7; 9; 0|];
|]

let damm str =
    let rec helper (v:string) interim =
        if v.Length = 0 then 0 = interim
        else helper (v.Substring(1)) (TABLE.[interim].[(int (v.[0])) - (int '0')])
    helper str 0

[<EntryPoint>]
let main _ =
    let numbers = [|5724; 5727; 112946; 112949|]
    for number in numbers do
        let isValid = damm (number.ToString())
        if isValid then
            printfn "%6d is valid" number
        else
            printfn "%6d is invalid" number

    0 // return an integer exit code