AoC 2022 - Day 25 🎄

Mix.install([:kino])

Setup

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

Part 1

defmodule Day25 do
  @int_carry_digit %{4 => {1, ?-}, 3 => {1, ?=}, 2 => {0, ?2}, 1 => {0, ?1}, 0 => {0, ?0}}

  def parse_number(num_str) do
    num_str
    |> String.split("", trim: true)
    |> Enum.reverse()
    |> get_snafu_value()
  end

  def to_snafu(x) when x >= 0 and x <= 2, do: [elem(@int_carry_digit[x], 1)]

  def to_snafu(sum) do
    {carry, digit} = @int_carry_digit[rem(sum, 5)]
    to_snafu(div(sum, 5) + carry) ++ [digit]
  end

  # Private method
  def get_snafu_value(snfu_inverted_list) do
    do_get_snafu_value(snfu_inverted_list, 0, 0)
  end

  def do_get_snafu_value([], _power_of, total) do
    # IO.inspect("reached end: " <> Integer.to_string(total))
    total
  end

  def do_get_snafu_value(["0" | rest], power_of, total) do
    # IO.inspect("got 0 in " <> Integer.to_string(power_of) <> " result: " <> Integer.to_string(0))
    do_get_snafu_value(rest, power_of + 1, total)
  end

  def do_get_snafu_value(["1" | rest], power_of, total) do
    # IO.inspect("got 1 in " <> Integer.to_string(power_of) <> " result: " <> Integer.to_string(5 ** power_of))
    do_get_snafu_value(rest, power_of + 1, total + 5 ** power_of)
  end

  def do_get_snafu_value(["2" | rest], power_of, total) do
    # IO.inspect("got 2 in " <> Integer.to_string(power_of) <> " result: " <> Integer.to_string(2 * (5 ** power_of)))
    do_get_snafu_value(rest, power_of + 1, total + 2 * 5 ** power_of)
  end

  def do_get_snafu_value(["-" | rest], power_of, total) do
    do_get_snafu_value(rest, power_of + 1, total + 5 ** power_of * -1)
  end

  def do_get_snafu_value(["=" | rest], power_of, total) do
    do_get_snafu_value(rest, power_of + 1, total + 5 ** power_of * -2)
  end
end

input
|> Kino.Input.read()
|> String.split("\n", trim: true)
|> Enum.map(&amp;Day25.parse_number/1)
|> Enum.sum()
|> Day25.to_snafu()