AoC

Day 3

# input = "xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))"
input = File.read!("3/input.txt")

defmodule U do
  def parse_mul([_, n1, n2]) do 
    {String.to_integer(n1), String.to_integer(n2)}
  end
end

r = ~r/mul\((\d{1,3}),(\d{1,3})\)/
r |> Regex.scan(input) |> Enum.map(&U.parse_mul/1) |> Enum.reduce(0, fn {a, b}, s -> s + (a * b) end)

Part 2

defmodule U2 do
  def parse_mul([_, "mul", n1, n2]) do 
    {:mul, String.to_integer(n1), String.to_integer(n2)}
  end
  
  def parse_mul([_, "", "", "", "do"]) do 
    :do
  end

  def parse_mul([_, "", "", "", "", "don't"]) do 
    :dont
  end
end

r = ~r/(mul)\((\d{1,3}),(\d{1,3})\)|(do)\(\)|(don't)\(\)/

r
|> Regex.scan(input)
|> Enum.map(&U2.parse_mul/1)
|> Enum.reduce(
  {0, true},
  fn
    {:mul, a, b}, {s, true} -> {s + a * b, true}
    {:mul, _, _}, {s, false} -> {s, false}
    :do, {s, _} -> {s, true}
    :dont, {s, _} -> {s, false}
  end
)