open Scanf

let handle_line line = sscanf line "%d   %d" (fun num1 num2 -> (num1, num2))
let sort_list l = List.sort compare l

let build_lists lines =
  let rec loop lines l1 l2 =
    match lines with
    | [] -> (l1, l2)
    | head :: tail ->
        let num1, num2 = handle_line head in
        loop tail (l1 @ [ num1 ]) (l2 @ [ num2 ])
  in
  loop lines [] [] |> fun (l1, l2) -> (sort_list l1, sort_list l2)

let find_occurances l item =
  let rec loop l item acc =
    match l with
    | [] -> acc
    | head :: tail ->
        if head == item then loop tail item (acc + 1) else loop tail item acc
  in
  loop l item 0

let solve lines =
  let rec distance l1 l2 acc =
    match (l1, l2) with
    | [], [] -> acc
    | h1 :: t1, h2 :: t2 ->
        distance t1 t2 (acc + if h1 > h2 then h1 - h2 else h2 - h1)
    | _, _ -> acc
  in

  let l1, l2 = build_lists lines in
  let part1 = distance l1 l2 0 in

  let rec similarity l1 l2 acc =
    match l1 with
    | [] -> acc
    | head :: tail -> similarity tail l2 (acc + (head * find_occurances l2 head))
  in

  let part2 = similarity l1 l2 0 in
  (part1, part2)