Advent of Code 2019 Day08

day08.exs

defmodule Day08 do
  @x 25
  @y 6

  def part1 do
    read_layers()
    |> Enum.min_by(fn layer -> length(Enum.filter(layer, &(&1 == ?0))) end)
    |> Enum.group_by(& &1)
    |> Map.take([?1, ?2])
    |> Map.values()
    |> (fn [a, b] -> length(a) * length(b) end).()
  end

  def part2 do
    read_layers()
    |> Enum.reduce(&merge/2)
    |> Enum.map(fn c -> if c == ?1, do: 0x2588, else: ' ' end)
    |> Enum.chunk_every(@x)
    |> Enum.intersperse("\n")
  end

  defp merge(down, top) do
    top
    |> Enum.zip(down)
    |> Enum.map(fn {top, down} -> if top != ?2, do: top, else: down end)
  end

  defp read_layers do
    "data/day08.txt"
    |> File.read!()
    |> String.trim()
    |> String.to_charlist()
    |> Enum.chunk_every(@x * @y)
  end
end

IO.puts("part 1: #{Day08.part1()}")
IO.puts("part 2:\n#{Day08.part2()}")