Get Loop and Tail lengths from Linked List

ItsFunctionalBro

open System.Text.RegularExpressions;

let buildList args =
    Regex.Matches(args, "(\d\,\s?\d)")
    |> Seq.cast<Match>
    |> Seq.map (fun m -> m.Value.Replace(" ", "").Split([|','|]))
    |> Seq.toList
 
let findDuplicatePointer list =
    let rec findCycleRec (oldList:list<array<string>>) (newList:list<array<string>>) =
        match oldList with
        | [] -> None
        | x::xs when List.exists (fun (i:array<string>) -> i.[0] = x.[1]) newList -> Some x
        | x::xs -> findCycleRec xs (x::newList)
    findCycleRec list []

let getListInfo list maybeElement =
    let index = 
        match maybeElement with
        | Some (x:array<string>) -> (List.findIndex (fun (i:array<string>) -> i.[1] = x.[1]) list)
        | None -> -1

    let tailLength = index + 1
    let loopLength = (List.length list) - tailLength
    (tailLength, loopLength)

let printListInfo listArgs =
    let list =  buildList listArgs
    let element = findDuplicatePointer list
    printfn "%A" (getListInfo list element)

[<EntryPoint>]
let main argv = 
    printListInfo "[1, 2], [2, 3], [3, 4], [4, 2]"
    printListInfo "[1, 2], [2, 3], [3, 4], [4, 5], [5, 6], [6, 3]"

    0 // return an integer exit code