Day 25

Setup

https://adventofcode.com/2022/day/25

defmodule Load do
  def input do
    File.read!(Path.join(Path.absname(__DIR__), "input/25.txt"))
  end
end

defmodule Parse do
  def input(input_str) do
    input_str
    |> String.split("\n", trim: true)
  end
end

test_input =
  """
  1=-0-2
  12111
  2=0=
  21
  2=01
  111
  20012
  112
  1=-1=
  1-12
  12
  1=
  122
  """
  |> Parse.input()

real_input =
  Load.input()
  |> Parse.input()

defmodule Day25 do
  def snafu_to_dec(snafu) do
    snafu
    |> String.split("", trim: true)
    |> Enum.map(fn char ->
      case char do
        "=" -> -2
        "-" -> -1
        "0" -> 0
        "1" -> 1
        "2" -> 2
      end
    end)
    |> Enum.reverse()
    |> Enum.reduce({0, 0}, fn int, {acc, pow} ->
      {acc + int * :math.pow(5, pow), pow + 1}
    end)
    |> elem(0)
    |> round
  end

  def dec_to_snafu(dec) do
    offset = 0
    base_5 = Integer.to_string(dec + offset, 5)

    {snafu, carry} =
      base_5
      |> String.graphemes()
      |> Enum.reverse()
      |> Enum.reduce({"", 0}, fn dec_str, {acc, carry} ->
        as_int = elem(Integer.parse(dec_str), 0)

        next_carry =
          cond do
            as_int + carry > 2 -> 1
            true -> 0
          end

        snafu_digit =
          case as_int + carry do
            0 -> "0"
            1 -> "1"
            2 -> "2"
            3 -> "="
            4 -> "-"
            5 -> "0"
          end

        {snafu_digit <> acc, next_carry}
      end)

    if(carry > 0, do: "1", else: "") <> snafu
  end
end

# Day25.dec_to_snafu(2022)
# Day25.snafu_to_dec("1121-1110-1=0")
# Day25.snafu_to_dec("1=11-2")
Day25.dec_to_snafu(4890)

Part 1

defmodule Part1 do
  def solve(input) do
    input
    |> Enum.map(&Day25.snafu_to_dec/1)
    |> Enum.sum()
    |> Day25.dec_to_snafu()
  end
end

Part1.solve(test_input)

Part1.solve(real_input)