fsharp-learning/exercism/fsharp/collatz-conjecture/CollatzConjecture.fs

module CollatzConjecture

let rec countSteps counter n =
    match n with
    | 1 -> counter
    | _ when n % 2 = 0 -> countSteps (counter + 1) (n / 2)
    | _ -> countSteps (counter + 1) (n * 3 + 1)

let steps (number: int): int option = 
    match number with
     | _ when number < 1 -> None
     | _ -> Some(countSteps 0 number)