Maximally functionalized imperative algo

task.ml

exception Enough

let n_ints_from_stdin ~n =
  let reader count =
    try
      if count = n then raise Enough else Some(read_int ())
    with
    | Enough -> None
    | err -> raise err
  in
  Stream.from reader

let loop ~n f =
  List.init n (fun _ -> ())
  |> List.to_seq
  |> Seq.iter f

let pair_of_n_ints ~n ~ints ~factor =
  let r = Array.make factor 0
  and left = ref 0
  and right = ref 0 in

  let process () =
    let a = Stream.next ints in
    let p = a mod factor in
    let mod_diff_index = (factor - p) mod factor in

    if r.(mod_diff_index) > a && r.(mod_diff_index) > (!left + !right)
    then (left := r.(mod_diff_index); right := a);

    if a > r.(p) then r.(p) <- a
  in
  loop ~n process;
  (!left, !right)

let () =
  let n = read_int () in
  let ints = n_ints_from_stdin ~n
  and factor = 120 in
  let (a, b) = pair_of_n_ints ~n ~ints ~factor in
  Printf.printf "(%i, %i)\n" a b