class Day06
  def initialize(filename)
    @filename = filename
  end

  def solve
    off_balance_trees = 0

    File.open(@filename).each("\r\n\r\n") do |tree|
      trunk = 0
      left = 0
      right = 0

      tree.strip.each_line.with_index do |line, i|
        if i.zero?
          # first line is trunk
          trunk = line.to_i
        elsif i == 1
          # second line is left and right branch weight
          l, r = line.split(' ')
          left = l.to_i
          right = r.to_i
        elsif i == 2
          # third line is 2 left and 2 right ornament weights
          line.each_line(' ').with_index do |weight, i|
            if i < 2
              left += weight.to_i
            elsif i < 4
              right += weight.to_i
            end
          end
        end
      end

      off_balance_trees += trunk + left + right if (left - right).abs > 1
    end.close

    puts "Off balance tree weight: #{off_balance_trees}"
  end
end

# Expects the input file to be named 06.txt and in the current working directory
if __FILE__ == $PROGRAM_NAME
  challenge = Day06.new('06.txt')
  challenge.solve
end

As the elves are busy making Christmas trees Mrs. Santa comes to look over the finished products. She notices that some of the Christmas trees are leaning one way or the other while some are straight as an arrow. She consults with the Head Elf and confirms that there is an issue in the production of Christmas trees. Help them figure out which trees are off balance so they know how much material is going to need to be recycled.

The elves today were making simple trees with only 2 branches and up to 2 ornaments on each branch. Each part of the tree has a specific weight.

• The trunk
• Each branch (just the bare branch, before it was decorated)
• Each ornament

Mrs. Santa has noted that the trees only start to lean over if the branches weights are off by more than 1.

The trees are given as input in the following format:

9
6 6
1 2 2 1

8
4 5
2 2 2 2

9
5 6
1 2 2 2

8
6 6
2 2 _ _

Each tree is separated by a blank line. Each tree is defined as such:

• The first line is the weight of the tree trunk
• The next line has the weight of the left branch and the right branch, in that order
• The last line has the weights of the ornaments. The first two are for the left branch, the last two are for the right branch.
  • If there is an underscore _ it means there is a missing ornament so don’t count it

Problem: Calculate the total weight of all the trees in trees.txt that are off balance. For the example above the total weight of off balance trees (the last 2) is 51.