Advent of Code 2023 day009.rb

day009.rb

require_relative "main"

module Day009
  INPUT = File.read('INPUT.txt')

  lines = INPUT.to_lines

  sets = lines.map do |line|
    line.split(" ").map(&:to_i)
  end

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

  t1 = 0
  t2 = 0
  sets.each do |set|
    layers = [set]

    target_layer = set
    loop do
      diffs = target_layer.each_cons(2).map do |a, b|
        b - a
      end

      layers.push(diffs)

      break if diffs.all?(0)

      target_layer = diffs
    end

    layers.last.push(0)
    layers.last.unshift(0)

    layers.reverse.each_cons(2) do |layer, layer_next|
      layer_next.push(layer.last + layer_next.last)
      layer_next.unshift(layer_next.first - layer.first)
    end

    t1 += set.last
    t2 += set.first
  end

  answer1 = t1

  pp answer1

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

  answer2 = t2

  pp answer2
end