day7.rb

day7.rb

input = File.readlines("inputs/day7.in")

DISCS = {}

class Disc < Struct.new(:name, :weight, :children, :parent)
  def subtree_weight
    return weight unless children
    children.map {|c| DISCS[c].subtree_weight}.inject(0) {|a,b| a+b} + weight
  end
end

input.each do |line|
  disc = if line =~ /^(\w+) \((\d+)\) -> (.+)$/
    Disc.new $1, $2.to_i, $3.split(',').map(&:strip)
  elsif line =~ /^(\w+) \((\d+)\)$/
    Disc.new($1, $2.to_i)
  end
  DISCS[disc.name] = disc
end

DISCS.values.each do |disc|
  children = disc.children
  next unless children
  children.each {|name| DISCS[name].parent = disc}
end

root = DISCS.values.detect {|d| d.parent.nil? }
puts "root: #{root.name}"


def find_element_with_other_weigth(root)
  hash = Hash.new {|h,k| h[k] = Array.new}
  root.children.each do | c|
    disc = DISCS[c]
    hash[disc.subtree_weight] << disc
  end
  key, value = hash.detect {|k,v| v.size == 1}
  if value
    find_element_with_other_weigth(value.first)
  else
    root
  end
end

wrong = find_element_with_other_weigth(root)
other_element = DISCS[wrong.parent.children.detect {|c| c != wrong.name}]

puts "correct weight: #{wrong.weight - (wrong.subtree_weight - other_element.subtree_weight)}"