Day 10: Monitoring Station

Mix.install([:kino])
input = Kino.Input.textarea("")

Part 1

asteroids =
  input
  |> Kino.Input.read()
  |> String.split("\n", trim: true)
  |> Enum.with_index()
  |> Enum.flat_map(fn {line, y} ->
    line
    |> String.to_charlist()
    |> Enum.with_index()
    |> Enum.flat_map(fn
      {?#, x} -> [{x, y}]
      _ -> []
    end)
  end)

{{x0, y0}, lines} =
  asteroids
  |> Enum.map(fn {x, y} = p ->
    {p,
     asteroids
     |> Enum.map(fn {x1, y1} -> {x1 - x, y1 - y} end)
     |> Enum.reject(&match?({0, 0}, &1))
     |> Enum.group_by(fn {x1, y1} -> :math.atan2(x1, y1) end)}
  end)
  |> Enum.max_by(fn {_, v} -> map_size(v) end)

map_size(lines)

Part 2

lines
|> Enum.sort(&Kernel.>=/2)
|> Enum.map(fn {_angle, asteroids} ->
  asteroids
  |> Enum.sort_by(fn {x, y} -> x ** 2 + y ** 2 end)
  |> Stream.concat(Stream.cycle([nil]))
end)
|> Stream.zip_with(& &1)
|> Stream.concat()
|> Stream.filter(& &1)
|> Enum.at(199)
|> then(fn {x, y} -> (x + x0) * 100 + y + y0 end)