Day 6

Deps & preparation

Mix.install([
  {:kino, "~> 0.4.0"}
])

input = Kino.Input.textarea("Please paste your input file:")

Input

start_state =
  Kino.Input.read(input)
  |> String.split([","], trim: true)
  |> Enum.map(&String.to_integer/1)
  |> Enum.frequencies()

Part 1

Enum.reduce(1..80, start_state, fn _, state ->
  state
  |> Enum.reduce(%{}, fn
    {0, c}, curr_state ->
      curr_state |> Map.update(6, c, &(c + &1)) |> Map.update(8, c, &(c + &1))

    {age, c}, curr_state ->
      curr_state |> Map.update(age - 1, c, &(c + &1))
  end)
end)
|> Map.values()
|> Enum.sum()

Part 2

Enum.reduce(1..256, start_state, fn _, state ->
  state
  |> Enum.reduce(%{}, fn
    {0, c}, curr_state ->
      curr_state |> Map.update(6, c, &(c + &1)) |> Map.update(8, c, &(c + &1))

    {age, c}, curr_state ->
      curr_state |> Map.update(age - 1, c, &(c + &1))
  end)
end)
|> Map.values()
|> Enum.sum()