day5

Mix.install([:kino])

Section

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

input = Kino.Input.read(input)

defmodule Recursion do
  def find_row(["F" | tail], {lower, upper}) do
    middle = Integer.floor_div(upper + lower, 2)
    find_row(tail, {lower, middle})
  end

  def find_row(["B" | tail], {lower, upper}) do
    middle = Integer.floor_div(upper + lower, 2)
    find_row(tail, {middle, upper})
  end

  def find_row(other, {_, upper}) do
    find_col(other, {0, 7}, upper)
  end

  def find_col(["L" | tail], {lower, upper}, row) do
    middle = Integer.floor_div(upper + lower, 2)
    find_col(tail, {lower, middle}, row)
  end

  def find_col(["R" | tail], {lower, upper}, row) do
    middle = Integer.floor_div(upper + lower, 2)
    find_col(tail, {middle, upper}, row)
  end

  def find_col([], {_, col}, row) do
    row * 8 + col
  end

  def find_gap([head | tail], nil) do
    find_gap(tail, head)
  end

  def find_gap([head | tail], prev) when head == prev + 1 do
    find_gap(tail, head)
  end

  def find_gap([head | _], prev) when head != prev + 1 do
    prev + 1
  end
end

part1 =
  input
  |> String.split()
  |> Enum.map(&String.graphemes(&1))
  |> Enum.map(&Recursion.find_row(&1, {0, 127}))
  |> Enum.max()
  |> IO.puts()

part2 =
  input
  |> String.split()
  |> Enum.map(&String.graphemes(&1))
  |> Enum.map(&Recursion.find_row(&1, {0, 127}))
  |> Enum.sort()
  |> Recursion.find_gap(nil)
  |> IO.puts()