open Core

(* Take text input from file and process accordingly *)
let process_input input = String.split_lines input |> List.map ~f:int_of_string

(* Fill in solutions for each part *)
let part_1 input =
  let freq_changes = process_input input in
  List.fold freq_changes ~init:0 ~f:(+)

let part_2 input =
  let freq_changes = process_input input |> Sequence.cycle_list_exn in
  let counter = Hashtbl.create (module Int) in
  let increment key = Hashtbl.update_and_return counter key 
    ~f:(function
        | Some num -> num + 1
        | None -> 1) in
  Sequence.fold_until freq_changes ~init:0 
    ~f:(fun sum freq ->
      if (increment (sum + freq)) = 2
      then
        Stop (sum + freq)
      else
        Continue (sum + freq))
    ~finish:(fun sum -> sum)