gistfile1.txt

class Integer
  def fibonacci
    a, b = 0, 1
    return self if self < 2
    2.upto(self) do
      a, b = b, a+b
    end
    b
  end
end


# How I walk most students through it:
class Integer
  def fibonacci
    a, b = 0, 1
    return self if self < 2
    (0..self).each do
      c = a + b
      a = b
      b = c
    end
    a + b
  end
end