Day 9

Section

defmodule Part1 do
  def example() do
    """
    0 3 6 9 12 15
    1 3 6 10 15 21
    10 13 16 21 30 45
    """

    File.read!("./adventofcode_2023/day9.txt")
    |> String.split("\n", trim: true)
  end

  def something(list) do
    sub_list =
      Enum.with_index(list)
      |> Enum.reduce([], fn {l, i}, acc ->
        Enum.at(list, i + 1)
        |> case do
          nil ->
            acc

          li ->
            acc ++ [li - l]
        end
      end)

    Enum.all?(sub_list, fn i -> i == 0 end)
    |> if do
      [sub_list]
    else
      ([list] ++ [sub_list] ++ something(sub_list))
      |> Enum.uniq()
    end
  end

  def get_num(list) do
    Enum.reverse(list)
    |> Enum.reduce(0, fn i, acc ->
      acc + List.last(i)
    end)
  end

  def get_num2(list) do
    list
    |> Enum.reverse()
    |> Enum.reduce([], fn i, acc ->
      a =
        List.last(acc)
        |> case do
          nil -> 0
          r -> r
        end

      y = List.first(i) - a

      acc ++ [y]
    end)
    |> List.last()
  end
end

Part1.example()
|> Enum.reduce(0, fn i, acc ->
  y =
    String.split(i, " ", trim: true)
    |> Enum.map(fn i -> String.to_integer(i) end)
    |> Part1.something()
    |> IO.inspect()
    |> Part1.get_num2()
    |> IO.inspect()

  acc + y
end)

[[10, 13, 16, 21, 30, 45], [3, 3, 5, 9, 15], [0, 2, 4, 6], [2, 2, 2], [0, 0]]
|> Enum.reverse()
|> IO.inspect()
|> Enum.reduce([], fn i, acc ->
  a =
    List.last(acc)
    |> case do
      nil -> 0
      r -> r
    end
    |> IO.inspect()

  y = List.first(i) - a

  IO.inspect({a, y})

  acc ++ [y]
end)
|> List.last()