AoC day 10 alternative

aoc_day10.fsx

let input = "3113322113"

let rec read acc lst =
    match lst, acc with
    | n::t, [] -> read [(1, n)] t
    | n::t, (count, lastNum)::t' when n = lastNum ->
        read ((count+1, lastNum)::t') t
    | n::t, _ ->
        read ((1, n)::acc) t
    | [], _ -> 
        acc 
        |> List.rev
        |> Seq.collect (fun (n, x) ->
            sprintf "%d%c" n x)
        |> fun xs -> System.String.Join("", xs)

{ 1..40 }
|> Seq.fold (fun last _ -> read [] (last |> Seq.toList)) input
|> Seq.length