🎄 Year 2024 🔔 Day 05

Setup

[rules, instructions] =
  File.read!("#{__DIR__}/../../../inputs/2024/day05.txt")
  |> String.split("\n\n", trim: true)

rules =
  String.split(rules, "\n", trim: true)
  |> Enum.map(&String.split(&1, "|", trim: true))
  |> Enum.map(fn [a, b] -> [String.to_integer(a), String.to_integer(b)] end)
  |> MapSet.new()

instructions =
  String.split(instructions, "\n", trim: true)
  |> Enum.map(&String.split(&1, ",", trim: true))
  |> Enum.map(&Enum.map(&1, fn e -> String.to_integer(e) end))

Part 1

instructions
|> Enum.filter(fn instruction_set ->
  instruction_set
  |> Enum.chunk_every(2, 1, :discard)
  |> Enum.all?(&MapSet.member?(rules, &1))
end)
|> Enum.map(fn instructions ->
  index = div(Enum.count(instructions), 2) + rem(Enum.count(instructions), 2) - 1
  Enum.at(instructions, index)
end)
|> Enum.sum()

Part 2

instructions
|> Enum.filter(fn instruction_set ->
  instruction_set
  |> Enum.chunk_every(2, 1, :discard)
  |> Enum.any?(fn rule -> !MapSet.member?(rules, rule) end)
end)
|> Enum.map(fn instruction_set ->
  Enum.sort(instruction_set, fn a, b -> MapSet.member?(rules, [a, b]) end)
end)
|> Enum.map(fn instructions ->
  index = div(Enum.count(instructions), 2) + rem(Enum.count(instructions), 2) - 1
  Enum.at(instructions, index)
end)
|> Enum.sum()