Day 06

Setup

Mix.install([
  {:kino, "~> 0.4.1"}
])

input = Kino.Input.textarea("Please enter your Input")

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

Part 1

defmodule Recursion1 do
  def recur(fishes), do: recur(fishes, [])
  defp recur([0 | fishes], children), do: [6 | recur(fishes, [8 | children])]
  defp recur([fish | fishes], children), do: [fish - 1 | recur(fishes, children)]
  defp recur([], children), do: children
end

1..80
|> Enum.reduce(fishes, fn _, fishes -> Recursion1.recur(fishes) end)
|> length()

Part 2

defmodule Recursion2 do
  def recur({day0, day1, day2, day3, day4, day5, day6, day7, day8}) do
    {day1, day2, day3, day4, day5, day6, day7 + day0, day8, day0}
  end
end

frequencies = Enum.frequencies(fishes)
amounts = Enum.map(0..8, fn i -> frequencies[i] || 0 end) |> List.to_tuple()

1..256
|> Enum.reduce(amounts, fn _, amounts -> Recursion2.recur(amounts) end)
|> Tuple.sum()