🎄 Year 2025 🔔 Day 07

Section

input =
  File.read!("#{__DIR__}/../../../inputs/2025/day07.txt")
  |> String.split("\n", trim: true)

Part 1

input
|> Enum.map(fn row -> row |> String.split("", trim: true) |> Enum.with_index() end)
|> Enum.reduce({MapSet.new(), 0}, fn row, acc ->
  Enum.reduce(row, acc, fn {c, i}, {beam_indexes, count} ->
    case c do
      "." -> {beam_indexes, count}
      "S" ->
        new_indexes = beam_indexes |> MapSet.put(i)
        {new_indexes, count}
      "^" ->
        if MapSet.member?(beam_indexes, i) do
          new_indexes = beam_indexes |> MapSet.delete(i) |> MapSet.put(i - 1) |> MapSet.put(i + 1)
          {new_indexes, count + 1}
        else
          {beam_indexes, count}
        end
    end
  end)
end)

Part 2

input
|> Enum.map(fn row -> row |> String.split("", trim: true) |> Enum.with_index() end)
|> Enum.reduce(Map.new(), fn row, quantum_map ->
  Enum.reduce(row, Map.new(), fn {c, i}, new_quantum_map ->
    count = Map.get(quantum_map, i, 0)
    case c do
      "." ->
        new_quantum_map
        |> Map.update(i, count, &(&1 + count))
      "S" ->
        new_quantum_map |> Map.put(i, 1)
      "^" ->
        new_quantum_map
        |> Map.update(i - 1, count, &(&1 + count))
        |> Map.update(i + 1, count, &(&1 + count))
    end
  end)
end)
|> Enum.sum_by(&elem(&1, 1))