let () = print_endline "hello"

let read_file_into_lists filename =
  let in_channel = open_in filename in
  let rec read_lines left right =
    try
      let line = input_line in_channel in
      match String.split_on_char '\t' line with
      | [l; r] ->
         read_lines (int_of_string l :: left) (int_of_string r :: right)
      | _ -> failwith "invalid line format"
    with End_of_file ->
      close_in in_channel;
      (List.rev left, List.rev right)
  in read_lines [] []

let () =
  let left_nums, right_nums = read_file_into_lists "d01.input" in
  Print.printf "Left numbers: %s\n" (String.concat " " (List.map string_of_int left_nums));
  Print.printf "Right numbers: %s\n" (String.concat " " (List.map string_of_int right_nums));;