Day 3: Mull It Over

Mix.install([:kino, :nimble_parsec])

Section

input = Kino.Input.text("Input", monospaced: true)

defmodule Instructions do
  import NimbleParsec

  number = integer(min: 1, max: 3)

  op_mult =
    ignore(string("mul("))
    |> concat(number)
    |> ignore(string(","))
    |> concat(number)
    |> ignore(string(")"))
    |> tag(:mul)

  op_do = ignore(string("do()")) |> tag(:do)

  op_dont = ignore(string("don't()")) |> tag(:dont)

  defparsec(
    :parser,
    eventually(choice([op_do, op_dont, op_mult]))
    |> repeat()
  )
end

input = Kino.Input.read(input) |> Instructions.parser() |> elem(1)

Enum.reduce(input, 0, fn
  {:mul, [l, r]}, acc -> acc + l * r
  _, acc -> acc
end)

Enum.reduce(input, 0, fn
  {:mul, [l, r]}, acc when acc >= 0 -> acc + l * r
  {:dont, []}, acc when acc >= 0 -> -1 * acc
  {:do, []}, acc -> abs(acc)
  _, acc -> acc
end)