let rec group xs =
  match xs with
  | [] -> []
  | x :: rest ->
    let rec collect cur acc tail =
      match tail with
      | [] -> (List.rev acc, [])
      | y :: ys ->
        if y = cur then collect cur (y :: acc) ys
        else (List.rev acc, y :: ys)
    in
    let (g, tail) = collect x [x] rest in
    g :: group tail

;;

let gs = group [1;1;2;2;2;3;1;1;4] in
List.length gs * 10 + List.length (List.nth gs 1)