Advent of Code 2024 day003.rb

day003.rb

require_relative "main"

module Day003
  INPUT = File.read('INPUT.txt')

  ##########
  # Part 1 #
  ##########
   
  MUL_REGEX = /mul\(\d+,\d+\)/

  mul_to_prod = ->(s) { s.split(',').map { _1.gsub(/[^\d]/, '').to_i }.reduce(:*) }

  answer1 = INPUT.scan(MUL_REGEX).sum(&mul_to_prod)
  
  pp answer1

  ##########
  # Part 2 #
  ##########

  fetch_indices = ->(string, regex) do
    i, ii = -1, []
    while (i = string.index(regex, i + 1))
      ii.push(i)
    end
    ii
  end

  mul_ii = fetch_indices.call(INPUT, MUL_REGEX)
  off_ii = fetch_indices.call(INPUT, /don't\(\)/)
  on_ii = fetch_indices.call(INPUT, /do\(\)/)

  i = 0
  answer2 = 0
  on = true
  while i < INPUT.length
    if mul_ii.first == i
      mul_i = mul_ii.shift
      answer2 += mul_to_prod.call(INPUT[mul_i..].match(MUL_REGEX)[0]) if on
    elsif off_ii.first == i
      on = false
      off_ii.shift
    elsif on_ii.first == i
      on = true
      on_ii.shift
    end

    i += 1
  end

  pp answer2
end