Advent of Code 2023 day008.rb

day008.rb

require_relative "main"

module Day008
  INPUT = File.read('INPUT.txt')

  lines = INPUT.to_lines
  instructions = lines.shift.chars
  lines.shift

  graph = lines.map do |line|
    parent, children_string = line.split_strip("=")
    children = children_string.split_strip(",").map(&:to_an)
    [parent, children]
  end.to_h

  SIDE = %w[L R]

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

  cursor1 = "AAA"
  i = 0
  loop do
    side = SIDE.index(instructions[i % instructions.length])

    cursor1 = graph[cursor1][side]
    break if cursor1 == "ZZZ"

    i += 1
  end

  answer1 = i + 1

  pp answer1

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

  cursors = graph.keys.filter do |parent|
    parent[-1] == "A"
  end

  sums = cursors.map do |cursor2|
    i = 0
    loop do
      side = SIDE.index(instructions[i % instructions.length])

      cursor2 = graph[cursor2][side]
      break if cursor2[-1] == "Z"

      i += 1
    end
    i + 1
  end

  answer2 = sums.lcm

  pp answer2
end