Advent of Code. Day 3.

advent-3.ex

### Part 1
move = fn x, y, dir ->
	case dir do
		">" -> {x + 1, y}
		"<" -> {x - 1, y}
		"^" -> {x, y + 1}
		"v" -> {x, y - 1}
	end
end

{_, _, set} = input |> String.codepoints |> Enum.reduce {0, 0, HashSet.new}, fn (dir, {x, y, set}) ->
	{x, y} = move.(x, y, dir)
	{x, y, HashSet.put(set, {x, y})}
end

IO.puts "Houses visited: #{HashSet.size set}"

### Part 2
{_, _, _, _, _, set} = input |> String.codepoints |> Enum.reduce {0, 0, 0, 0, :santa, HashSet.new}, fn (dir, {santa_x, santa_y, robo_x, robo_y, who, set}) ->
	case who do
		:santa ->
			{santa_x, santa_y} = move.(santa_x, santa_y, dir)
			{santa_x, santa_y, robo_x, robo_y, :robo, HashSet.put(set, {santa_x, santa_y})}

		:robo ->
			{robo_x, robo_y} = move.(robo_x, robo_y, dir)
			{santa_x, santa_y, robo_x, robo_y, :santa, HashSet.put(set, {robo_x, robo_y})}
	end
end

IO.puts "Houses visited (santa + robot): #{HashSet.size set}"