gistfile1.rb

class CollatzSequence
  include Enumerable

  def initialize(n)
    @n = n
  end

  def each
    n = @n
    yield n
    while n > 1
#      n = n.even? ? n / 2 : n * 3 + 1
      if n.even?
        n = n / 2
      else
        n = n * 3 + 1
      end
      yield n
    end
  end
end

class Foo < Struct.new(:start, :length, :sequence)
  include Comparable
  def <=>(other)
    self.length <=> other.length
  end

  def self.create_without_sequence(n)
    Foo.new(n, CollatzSequence.new(n).count)
  end

  def self.create(n)
    seq = CollatzSequence.new(n).to_a
    Foo.new(n, seq.length, seq)
  end
end

longest = (1 .. 1e6).map{|i| Foo.create_without_sequence(i)}.sort.last
p CollatzSequence.new(longest.start).to_a
puts longest.length