Day 6

Mix.install([
  {:req, "~> 0.3.2"},
  {:vega_lite, "~> 0.1.6"},
  {:kino_vega_lite, "~> 0.1.6"}
])

alias VegaLite, as: Vl

day = 6

aoc_session = System.fetch_env!("LB_AOC_SESSION")
input_url = "https://adventofcode.com/2022/day/#{day}/input"
{:ok, %{body: input}} = Req.get(input_url, headers: [cookie: "session=#{aoc_session}"])

Input

test_input = ~w(
  mjqjpqmgbljsphdztnvjfqwrcgsmlb 
  bvwbjplbgvbhsrlpgdmjqwftvncz
  nppdvjthqldpwncqszvftbrmjlhg
  nznrnfrfntjfmvfwmzdfjlvtqnbhcprsg
  zcfzfwzzqfrljwzlrfnpqdbhtmscgvjw
)

Part 1

defmodule Part1 do
  def start_of_packet_marker_pos(str, i \\ 4) do
    {header, rest} = String.split_at(str, 4)
    [_ | last3] = header_chars = String.graphemes(header)

    if all_uniq(header_chars),
      do: i,
      else: start_of_packet_marker_pos(Enum.join(last3) <> rest, i + 1)
  end

  defp all_uniq(lst), do: Enum.uniq(lst) == lst
end

for str <- test_input, do: Part1.start_of_packet_marker_pos(str)

Part1.start_of_packet_marker_pos(input)

Part 2

defmodule Part2 do
  def start_of_message_marker_pos(str, i \\ 14) do
    {header, rest} = String.split_at(str, 14)
    [_ | last13] = header_chars = String.graphemes(header)

    if all_uniq(header_chars),
      do: i,
      else: start_of_message_marker_pos(Enum.join(last13) <> rest, i + 1)
  end

  defp all_uniq(lst), do: Enum.uniq(lst) == lst
end

for str <- test_input, do: Part2.start_of_message_marker_pos(str)

Part2.start_of_message_marker_pos(input)