euler2

euler2.rb

#!/usr/bin/env ruby
# -*- coding: utf-8 -*-

fib = Enumerator.new do |y|
  a, b = 0, 1
  while b < 4000000 do
    y << b if b % 2 == 0
    a, b = b, a + b
  end
end

puts fib.inject{ |sum, n| sum + n }