Day 11: Plutonian Pebbles

Mix.install([:kino])

Section

input = Kino.Input.text("Input", monospace: true)

input =
  input
  |> Kino.Input.read()
  |> String.split()
  |> Enum.map(&String.to_integer/1)
  |> Enum.frequencies()

defmodule PlutonianPebble do
  def blink(%{} = map) do
    for {n, count} <- map,
        numbers <- blink(n),
        reduce: %{} do
      acc -> Map.update(acc, numbers, count, fn c -> count + c end)
    end
  end

  def blink(0), do: [1]

  def blink(n) do
    case Integer.digits(n) do
      numbers when rem(length(numbers), 2) == 0 ->
        numbers
        |> Enum.split(div(length(numbers), 2))
        |> then(fn {l, r} ->
          [Integer.undigits(l), Integer.undigits(r)]
        end)

      _ ->
        [n * 2024]
    end
  end

  def blinker(input) do
    Stream.unfold(input, fn n -> {n, PlutonianPebble.blink(n)} end)
  end
end

PlutonianPebble.blinker(input)
|> Enum.at(25)
|> Map.values()
|> Enum.sum()

PlutonianPebble.blinker(input)
|> Enum.at(75)
|> Map.values()
|> Enum.sum()