aoc-2020/01/main.ml

open Base

(* load the provided filename *)
let load_list filename =
  let open Stdio.In_channel in
  let lines = with_file ~f:input_lines filename
  in List.map ~f:Int.of_string lines

(* You might notice that this isn't actually >>=: I just wanted to
   have a non-parenthesized foreach! *)
let (>>=) list fn = let _ = List.map ~f:fn list in None

let print_result = function
  | None -> Stdio.printf "Unable to find result\n"
  | Some xs ->
     let lst = String.concat ~sep:" * " (List.map ~f:Int.to_string xs)
     in Stdio.printf "Got (%s) = %d\n" lst (List.fold ~init:1 ~f:(fun x y -> x * y) xs)

let part_one source =
  With_return.with_return (fun r ->
    source >>= fun a ->
    source >>= fun b ->
      if a <> b && a + b = 2020 then r.return (Some [a; b])
    )

let part_two source =
  With_return.with_return (fun r ->
    source >>= fun a ->
    source >>= fun b ->
    source >>= fun c ->
      if a <> b && b <> c && a <> c && a + b + c = 2020 then r.return (Some [a; b; c])
    )

let main() =
  let source = load_list "input" in
  print_result (part_one source);
  print_result (part_two source)

let () = main()