🎄 Year 2016 🔔 Day 02

Setup

input =
  File.read!("#{__DIR__}/../../../inputs/2016/day02.txt")
  |> String.split("\n", trim: true)
  |> Enum.map(&String.graphemes/1)

dir_coords = %{
  "U" => {0, -1},
  "D" => {0, 1},
  "L" => {-1, 0},
  "R" => {1, 0}
}

Part 1

keypad = %{
  {0, 0} => "1",
  {1, 0} => "2",
  {2, 0} => "3",
  {0, 1} => "4",
  {1, 1} => "5",
  {2, 1} => "6",
  {0, 2} => "7",
  {1, 2} => "8",
  {2, 2} => "9"
}

input
|> Enum.map_reduce({1, 1}, fn steps, start_coords ->
  end_coords =
    Enum.reduce(steps, start_coords, fn dir, {x, y} ->
      {mov_x, mov_y} = Map.fetch!(dir_coords, dir)

      new_x = x + mov_x
      new_y = y + mov_y

      if new_x < 0 || new_x > 2 || new_y < 0 || new_y > 2 do
        {x, y}
      else
        {new_x, new_y}
      end
    end)

  {end_coords, end_coords}
end)
|> elem(0)
|> Enum.map(&amp;Map.fetch!(keypad, &amp;1))
|> Enum.join()

Part 2

keypad = %{
  {2, 0} => "1",
  {1, 1} => "2",
  {2, 1} => "3",
  {3, 1} => "4",
  {0, 2} => "5",
  {1, 2} => "6",
  {2, 2} => "7",
  {3, 2} => "8",
  {4, 2} => "9",
  {1, 3} => "A",
  {2, 3} => "B",
  {3, 3} => "C",
  {2, 4} => "D"
}

input
|> Enum.map_reduce({1, 1}, fn steps, start_coords ->
  end_coords =
    Enum.reduce(steps, start_coords, fn dir, {x, y} ->
      {mov_x, mov_y} = Map.fetch!(dir_coords, dir)

      new_x = x + mov_x
      new_y = y + mov_y

      if (new_x == 0 && new_y == 2) ||
           (new_x == 1 &amp;&amp; (new_y >= 1 &amp;&amp; new_y <= 3)) ||
           (new_x == 2 &amp;&amp; (new_y >= 0 &amp;&amp; new_y <= 4)) ||
           (new_x == 3 &amp;&amp; (new_y >= 1 &amp;&amp; new_y <= 3)) ||
           (new_x == 4 &amp;&amp; new_y == 2) do
        {new_x, new_y}
      else
        {x, y}
      end
    end)

  {end_coords, end_coords}
end)
|> elem(0)
|> Enum.map(&amp;Map.fetch!(keypad, &amp;1))
|> Enum.join()