Day 13

Mix.install([
  {:nx, "~> 0.5"},
  {:kino, "~> 0.11.3"}
])

Section

input = Kino.Input.textarea("Input")

defmodule Sol13 do
  def read(text) do
    for test_case <- String.split(text, "\n\n") do
      for row <- String.split(test_case, "\n") do
        String.to_charlist(row)
      end
    end
  end

  def compare_diff(left, right) do
    for {x, y} <- Enum.zip(left, right) do
      if x == y, do: 0, else: 1
    end
    |> Enum.sum()
  end

  def find_mirror(data, accept_diff) do
    n = length(data)

    Enum.reduce_while(1..(n - 1), 0, fn idx, _ ->
      part_length = min(idx, n - idx)
      upper_part = Enum.slice(data, idx - part_length, part_length) |> Enum.concat()
      lower_part = Enum.slice(data, idx, part_length) |> Enum.reverse() |> Enum.concat()
      diff = compare_diff(upper_part, lower_part)

      if accept_diff == diff do
        {:halt, idx}
      else
        {:cont, 0}
      end
    end)
  end
end

input_data = Kino.Input.read(input)
test_cases = Sol13.read(input_data)
row_score = Enum.map(test_cases, &amp;Sol13.find_mirror(&amp;1, 1))
col_score = Enum.map(test_cases, &amp;Sol13.find_mirror(Enum.zip_with(&amp;1, fn x -> x end), 1))
Enum.sum(row_score) * 100 + Enum.sum(col_score)

String.to_charlist("AA..") -- String.to_charlist("..AA")