Advent of Code 2023 Day 13 Part 2

Mix.install([
  {:kino_aoc, "~> 0.1"},
  {:nx, "~> 0.9.2"}
])

Get Inputs

{:ok, puzzle_input} =
  KinoAOC.download_puzzle("2023", "13", System.fetch_env!("LB_SESSION"))

My answer

blocks =
  puzzle_input
  |> String.split("\n\n")
  |> Enum.map(fn block ->
    block
    |> String.split("\n")
    |> Enum.map(fn row ->
      String.codepoints(row)
      |> Enum.map(fn tile -> if tile == "#", do: 1, else: 0 end)
    end)
    |> Nx.tensor()
  end)

blocks
|> Enum.map(fn block ->
  0..1
  |> Enum.map(fn axis ->
    num = Nx.shape(block) |> elem(axis)

    0..(num - 2)
    |> Enum.find(fn index ->
      range = min(index + 1, num - index - 1)

      Nx.not_equal(
        Nx.slice_along_axis(block, index - range + 1, range, axis: axis),
        Nx.slice_along_axis(block, index + 1, range, axis: axis) |> Nx.reverse(axes: [axis])
      )
      |> Nx.sum()
      |> Nx.to_number()
      |> Kernel.==(1)
    end)
    |> then(fn index -> if is_nil(index), do: 0, else: index + 1 end)
    |> then(fn num -> if axis == 0, do: num * 100, else: num end)
  end)
  |> Enum.sum()
end)
|> Enum.sum()