one_eighth_heavier.rb

###
# 16.
#     You have eight balls all of the same size. 7 of them weigh the same, and one of them weighs slightly more.
#     How can you find the ball that is heavier by using a balance and only two weighings?
###

module Generator
  def self.generate_heavier_index(max=8)
    Time.now.sec.modulo(max)
  end
end

class Ball
  attr_accessor :index

  def initialize(index, is_heavy)
    @index = index
    @is_heavy = index == is_heavy
  end

  def heavy?
    @is_heavy
  end
end

class Balance
  MAX_WEIGHING_TIME = 2

  def initialize
    @count = 0
  end

  def weighing(left, right)
    count_up!
    _left = Array(left)
    _right = Array(right)

    case
    when !_left.find(&:heavy?).nil?
      1
    when !_right.find(&:heavy?).nil?
      -1
    else
      0
    end
  end

  def heavier?(left, right)
    count_up!

    return left  unless Array(left).find(&:heavy?).nil?
    return right unless Array(right).find(&:heavy?).nil?
    nil
  end

  def count_up!
    raise "You have already been weighing 2 times" if @count > MAX_WEIGHING_TIME
    @count += 1
  end
end


heavier_index = Generator.generate_heavier_index
balls = 8.times.map{|i| Ball.new(i, heavier_index)  }
_balls = balls.dup
balance = Balance.new

heaviers  = balance.heavier?(balls.pop(3), balls.pop(3)) || balls
heavy_one = balance.heavier?(heaviers.pop, heaviers.pop) || heaviers.pop

puts <<EOM
Concluded: heavy ball's index maybe #{ heavy_one.index }.
Actually : heavy ball's index is #{ heavier_index }.
EOM