aoc-2020/01/main.ml

open Base

let sample_list : int list = [
    1721;
    979;
    366;
    299;
    675;
    1456;
]

(* load the provided filename *)
let load_list (filename : string) : int list =
  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 part_one source =
  let res = Base.With_return.with_return (fun r ->
    source >>= fun a ->
    source >>= fun b ->
      if a <> b && a + b = 2020 then r.return (Some (a, b))
    ) in
  match res with
  | None -> Stdio.printf "Unable to find result\n"
  | Some (x, y) -> Stdio.printf "Got (%d * %d) = %d\n" x y (x * y)

let part_two source =
  let res = Base.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))
    ) in
  match res with
  | None -> Stdio.printf "Unable to find result\n"
  | Some (x, y, z) ->
     Stdio.printf "Got (%d * %d * %d) = %d\n" x y z (x * y * z)

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

let () = main()