AoC 2023 Day 9

Section

defmodule MirageMaintenance do
  def next_value(history) do
    case Enum.all?(history, &(&1 == 0)) do
      true -> 0
      false -> List.last(history) + (history |> differences() |> next_value())
    end
  end

  def differences(list), do: differences(list, [])

  defp differences([_], acc), do: Enum.reverse(acc)
  defp differences([a, b | rest], acc), do: differences([b | rest], [b - a | acc])
end

MirageMaintenance.differences([1, 2, 4, 7])

MirageMaintenance.next_value([0, 3, 6, 9, 12, 15])

MirageMaintenance.next_value([1, 3, 6, 10, 15, 21])

MirageMaintenance.next_value([10, 13, 16, 21, 30, 45])