Advent of Code - Day 6

Part 1

input = File.read!("inputs/day6.txt")

input
|> String.graphemes()
|> Enum.with_index(1)
|> Enum.reduce_while(
  [],
  fn {c, i}, l ->
    case Enum.uniq([c | l]) do
      new_l when length(new_l) == 4 -> {:halt, i}
      _ -> {:cont, Enum.take([c | l], 3)}
    end
  end
)

(input
 |> String.to_charlist()
 |> Stream.chunk_every(4, 1, :discard)
 |> Enum.find_index(&(&1 |> Enum.uniq() |> length == 4))) + 4

Part2

input
|> String.graphemes()
|> Enum.with_index(1)
|> Enum.reduce_while(
  [],
  fn {c, i}, l ->
    case Enum.uniq([c | l]) do
      new_l when length(new_l) == 14 -> {:halt, i}
      _ -> {:cont, Enum.take([c | l], 13)}
    end
  end
)

(input
 |> String.to_charlist()
 |> Stream.chunk_every(14, 1, :discard)
 |> Enum.find_index(&(&1 |> Enum.uniq() |> length == 14))) + 14

input
|> String.to_charlist()
|> Stream.chunk_every(14, 1, :discard)
|> Stream.with_index(15)
|> Stream.take_while(fn {l, _i} -> l |> Enum.uniq() |> length() != 14 end)
|> Stream.take(-1)
|> Enum.to_list()
|> hd()
|> elem(1)

defmodule Day6 do
  # patternmatching fun!
  # l = the list of chars, p = position where we are in the list
  # s = the size of consecutive non-repetitive chars we're looking for
  def find_marker(l, p, s), do: find_marker(l, p, s, length(Enum.uniq(Enum.take(l, s))))
  def find_marker(_, p, s, s), do: p + s
  def find_marker(l, p, s, _), do: find_marker(tl(l), p + 1, s)
end

input
|> String.to_charlist()
|> Day6.find_marker(0, 4)