digit5.ml

(* To build: corebuild digit5.native *)
(* To test-run: seq 10000 99999 |./digit5.native *)

open Core.Std

type t = int Char.Map.t
let empty = Char.Map.empty

let rec read_loop proc =
  match In_channel.input_line In_channel.stdin with
  | Some str -> proc str; read_loop proc
  | None -> ()
;;

let look_for_pair str =
  let rec f m l pair_flag =
    if List.is_empty l then
      pair_flag
    else
      let h = List.hd_exn l in
      match Map.find m h with
      | Some n ->
         (match n with
          | 2 -> false
          | 1 -> if pair_flag
                 then false
                 else f (Map.add m ~key:h ~data:2)
                        (List.tl_exn l) true
          | _ -> false)
      | None -> f (Map.add m ~key:h ~data:1) (List.tl_exn l) false
  in f Char.Map.empty (String.to_list str) false
;;

let lfp_front_end str =
  if look_for_pair str
  then printf "%s: good\n%!" str
  else printf "%s: bad\n%!" str
;;

read_loop lfp_front_end