Day 6

Setup

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

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

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

# convert lines to list of tuples with four intergers
# [{0, 1, 2, 3},...]
lines =
  input
  |> Kino.Input.read()
  |> String.split(",", trim: true)
  |> Enum.map(&String.to_integer/1)

Part 1

defmodule Fish do
  def process(_current_day = [], next_day, _new_fish = 0) do
    next_day
  end

  def process(_current_day = [], next_day, new_fish) do
    Enum.reduce(0..(new_fish - 1), next_day, fn _, next_day -> [8 | next_day] end)
  end

  def process(current_day, next_day, new_fish) do
    [fish | tail] = current_day

    cond do
      fish == 0 -> process(tail, [6 | next_day], new_fish + 1)
      fish -> process(tail, [fish - 1 | next_day], new_fish)
    end
  end
end

lines = Enum.reverse(lines)

Enum.reduce(0..17, lines, fn _, lines ->
  Fish.process(lines, [], 0)
end)
|> Enum.count()

Part 2

defmodule Fish2 do
  def process({p0, p1, p2, p3, p4, p5, p6, p7, p8}) do
    # IO.puts(inspect({p0, p1, p2, p3, p4, p5, p6, p7, p8}))
    {p1, p2, p3, p4, p5, p6, p7 + p0, p8, p0}
  end
end

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

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

1..80
|> Enum.reduce(amounts, fn _, amounts -> Fish2.process(amounts) end)
|> Tuple.sum()