class SolutionTwo < Problem

  def initialize()
    @memoized = []
  end

  def fibonacci(x)
    @memoized[x] ||= x <= 1 ? x : fibonacci(x - 2) + fibonacci(x - 1)
  end

  def sequence()
    1.upto(Float::INFINITY).lazy.map {|x| fibonacci(x)}.take_while {|x| x < 4000000}.select {|x| x.even?}
  end

  def solve()
    sequence.sum
  end
end