let count_words text =
  let words = String.split_on_char ' ' text in
  let counts = Hashtbl.create 8 in
  List.iter (fun w ->
    let n = match Hashtbl.find_opt counts w with
            | Some n -> n + 1
            | None -> 1
    in
    Hashtbl.replace counts w n
  ) words;
  counts

let max_count counts =
  Hashtbl.fold (fun _ v acc -> if v > acc then v else acc) counts 0

;;

max_count (count_words "the quick brown fox jumps over the lazy dog the fox")