Advent of Code. Day 6 - Part 1.

advent-6-part1.ex

parse_command = fn command ->
	{cmd, rest} = case command do
		<<"turn on ", rest :: binary>> -> {:on, rest}
		<<"turn off ", rest :: binary>> -> {:off, rest}
		<<"toggle ", rest :: binary>> -> {:toggle, rest}
	end

	[x1y1, _, x2y2] = String.split(rest)
	[x1, y1] = String.split(x1y1, ",") |> Enum.map(&(String.to_integer(&1)))
	[x2, y2] = String.split(x2y2, ",") |> Enum.map(&(String.to_integer(&1)))

	{cmd, min(x1, x2), min(y1, y2), max(x1, x2), max(y1, y2) }
end

generate_coordinates = fn x1, y1, x2, y2 ->
	Enum.flat_map(x1..x2, fn x ->
		Enum.map(y1..y2, fn y ->
			{x, y}
		end)
	end)
end

fill_map = fn map, cmd, x1, y1, x2, y2 ->
	Enum.reduce(generate_coordinates.(x1, y1, x2, y2), map, fn {x, y}, map ->
		map = case cmd do
			:on -> Dict.put(map, {x, y}, true)
			:off -> Dict.put(map, {x, y}, false)
			:toggle -> Dict.update(map, {x, y}, true, &(!&1))
		end
		map
	end)
end

input_stream = File.stream!("input.txt")

final_map = Enum.reduce(input_stream, %{}, fn line, light_map ->
	{cmd, x1, y1, x2, y2} = parse_command.(line |> String.strip)
	light_map = fill_map.(light_map, cmd, x1, y1, x2, y2)
	light_map
end)

lights_on = Enum.count(final_map, fn {_, val} -> val end)

IO.puts "Total number of lights on: #{lights_on}"