Advent of Code 2024 day005.rb

day005.rb

require_relative "main"

module Day005
  INPUT = File.read('INPUT.txt')

  rules_raw, updates_raw = INPUT.split("\n\n")

  rules = rules_raw.split("\n").map { _1.split("|").map(&:to_i) }
  updates = updates_raw.split("\n").map { _1.split(",").map(&:to_i) }

  yea = rules.each_with_object(Hash.new { |h, k| h[k] = [] }) { _2[_1[0]].push(_1[1]) }
  nay = rules.each_with_object(Hash.new { |h, k| h[k] = [] }) { _2[_1[1]].push(_1[0]) }

  ##########
  # Part 1 #
  ##########

  VALID = true
  INVALID = false

  segmented = updates.group_by do |u|
    is_invalid = false
    i = 0
    a = yea[u[i]]
    b = nay[u[i]]

    loop do
      break if (i += 1) == u.length || (is_invalid = !a.include?(u[i]) || b.include?(u[i]))
      a += yea[u[i]]
      b += nay[u[i]]
    end

    !is_invalid
  end

  answer1 = segmented[VALID].sum { _1[_1.length / 2] }

  pp answer1

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

  answer2 = segmented[INVALID].sum do |u|
    i = 0
    while i < u.length
      j = i + 1
      while j < u.length
        a = yea[u[i]]
        b = nay[u[i]]
        u[i], u[j] = u[j], u[i] if !a.include?(u[j]) || b.include?(u[j])
        j += 1
      end
      i += 1
    end

    u[u.length / 2]
  end

  pp answer2
end