99-problems.ml

(* Mine *)
let encode list =
  let rec encode' current acc list =
    match (current, list) with
    | (None, []) -> acc
    | (Some c, []) -> c::acc
    | (None, h::t) -> encode' (Some (1, h)) acc t
    | (Some ((count, elem) as c), h::t) -> if elem = h
                                           then encode' (Some (count+1, elem)) acc t
                                           else encode' (Some (1, h)) (c::acc) t
  in List.rev (encode' None [] list);;

(* Theirs *)
let encode list =
  let rec aux count acc = function
    | [] -> [] (* Can only be reached if original list is empty *)
    | [x] -> (count+1, x) :: acc
    | a :: (b :: _ as t) -> if a = b then aux (count + 1) acc t
                            else aux 0 ((count+1,a) :: acc) t in
  List.rev (aux 0 [] list);;