Day 3

Solution

{:ok, input} = File.read("#{__DIR__}/inputs/day03.txt")

mul = fn [_, a, b] -> String.to_integer(a) * String.to_integer(b) end

~r/mul\((\d+),(\d+)\)/
|> Regex.scan(input)
|> Enum.map(mul)
|> Enum.sum()

~r/mul\((\d+),(\d+)\)|do\(\)|don't\(\)/
|> Regex.scan(input)
|> Enum.reduce({0, true}, fn matches, {acc, enabled} ->
  cond do
    hd(matches) == "do()"    -> {acc, true}
    hd(matches) == "don't()" -> {acc, false}
    enabled                  -> {acc + mul.(matches), enabled}
    not enabled              -> {acc, enabled}
  end
end)