Day 9: Rope Bridge

Mix.install([{:kino, "~> 0.8.0"}, {:kino_bumblebee, "~> 0.1.0"}, {:exla, "~> 0.4.1"}],
  config: [nx: [default_backend: EXLA.Backend]]
)

Input

input = Kino.Input.textarea("Please insert your input")

moves =
  input
  |> Kino.Input.read()
  |> String.split(["\n", " "], trim: true)
  |> Enum.chunk_every(2)
  |> Enum.map(fn [dir, count] -> {dir, String.to_integer(count)} end)

Part 1 - Tailgating

defmodule Tailgater do
  defp move_x("R"), do: 1
  defp move_x("L"), do: -1
  defp move_x(_), do: 0

  defp move_y("U"), do: 1
  defp move_y("D"), do: -1
  defp move_y(_), do: 0

  def delta_tx(dx, _) when dx <= -2, do: 1
  def delta_tx(dx, _) when dx >= 2, do: -1
  # diagonal moves
  def delta_tx(-1, -2), do: 1
  def delta_tx(1, -2), do: -1
  def delta_tx(1, 2), do: -1
  def delta_tx(-1, 2), do: 1
  def delta_tx(_, _), do: 0

  defp delta_ty(_, dy) when dy <= -2, do: 1
  defp delta_ty(_, dy) when dy >= 2, do: -1
  # diagonal moves
  defp delta_ty(-2, -1), do: 1
  defp delta_ty(-2, 1), do: -1
  defp delta_ty(2, 1), do: -1
  defp delta_ty(2, -1), do: 1
  defp delta_ty(_, _), do: 0

  def move([], _, _, visited), do: visited

  def move([{cmd, 1} | moves], {hx, hy}, {tx, ty}, visited) do
    # move head to new pos
    new_hx = hx + move_x(cmd)
    new_hy = hy + move_y(cmd)

    new_tx = tx + delta_tx(tx - new_hx, ty - new_hy)
    new_ty = ty + delta_ty(tx - new_hx, ty - new_hy)

    new_visited = MapSet.put(visited, {new_tx, new_ty})

    move(moves, {new_hx, new_hy}, {new_tx, new_ty}, new_visited)
  end

  def move([{cmd, n} | moves], h, t, visited) do
    move([{cmd, 1}, {cmd, n - 1} | moves], h, t, visited)
  end
end

Tailgater.move(moves, {0, 0}, {0, 0}, MapSet.new([{0, 0}])) |> Enum.count()

Part 2: Rope snaps

This level beat me…, got the solution from mario melo’s github

https://github.com/mariomelo/advent_of_code_2022