🎄 Year 2022 🔔 Day 02

Parse input

filename = "#{__DIR__}/../../../inputs/2022/day02.txt"

parsed_input_stream =
  File.stream!(filename)
  |> Enum.map(&String.trim/1)
  |> Enum.map(&String.split/1)

Shared code

Part One

defmodule Helper do
  def calculate_score({l, r}) do
    options = String.graphemes("ABCABC")
    ri = Enum.find_index(options, &(&1 == r))

    cond do
      l == Enum.at(options, ri + 1) ->
        0 + choice_score(r)

      l == r ->
        3 + choice_score(r)

      l == Enum.at(options, ri - 1) ->
        6 + choice_score(r)
    end
  end

  defp choice_score("A"), do: 1
  defp choice_score("B"), do: 2
  defp choice_score("C"), do: 3
end

mappings = %{"X" => "A", "Y" => "B", "Z" => "C"}

parsed_input_stream
|> Enum.map(fn [l, r] -> {l, mappings[r]} end)
|> Enum.map(&Helper.calculate_score/1)
|> Enum.sum()

Part two

options = String.graphemes("ABCABC")
choice_score = fn choice -> Enum.find_index(String.graphemes("ABC"), &(&1 == choice)) + 1 end

parsed_input_stream
|> Enum.map(fn [l, r] ->
  li = Enum.find_index(options, &(&1 == l))

  case r do
    "X" ->
      0 + choice_score.(Enum.at(options, li - 1))

    "Y" ->
      3 + choice_score.(l)

    "Z" ->
      6 + choice_score.(Enum.at(options, li + 1))
  end
end)
|> Enum.sum()