Day 3

Part 1

sample = "xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))"

Regex.scan(~r/mul\((\d*),(\d*)\)/, sample)
|> Enum.map(fn [_, left, right] -> 
  String.to_integer(left) * String.to_integer(right)
end)
|> Enum.sum

sample = File.read!("priv/day3.txt")

Regex.scan(~r/mul\((\d*),(\d*)\)/, sample)
|> Enum.map(fn [_, left, right] -> 
  String.to_integer(left) * String.to_integer(right)
end)
|> Enum.sum

Part 2

sample = "xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))"

defmodule Part2 do
  def transform(parsed) do
    do_transform(parsed, true, [])
  end

  defp do_transform([], _, acc), do: Enum.reverse(acc)

  defp do_transform([["don't()"] | t], _, acc), do: do_transform(t, false, acc)

  defp do_transform([["do()"] | t], _, acc), do: do_transform(t, true, acc)

  defp do_transform([_ | t], false, acc), do: do_transform(t, false, acc)

  defp do_transform([h | t], true, acc), do: do_transform(t, true, [h | acc])
end

parsed = Regex.scan(~r/don't\(\)|do\(\)|mul\((\d*),(\d*)\)/, sample)

Part2.transform(parsed)
|> Enum.map(fn [_, left, right] -> 
  String.to_integer(left) * String.to_integer(right)
end)
|> Enum.sum

sample = File.read!("priv/day3.txt")

parsed = Regex.scan(~r/don't\(\)|do\(\)|mul\((\d*),(\d*)\)/, sample)

Part2.transform(parsed)
|> Enum.map(fn [_, left, right] -> 
  String.to_integer(left) * String.to_integer(right)
end)
|> Enum.sum