Fibonacci super efficiently

Fibonacci efficient

class Integer

    def fibonacci(arr=[0,1])
        arr[self] ||= (self-1).fibonacci(arr) + (self-2).fibonacci(arr)

        # if arr[self].nil?
        #          arr[self] = (self-1).fibonacci(arr) + (self-2).fibonacci(arr)
        #        end
        #        arr[self]



        #arr[self] ||= (self-1).fibonacci(arr) + (self-2).fibonacci(arr)
        # return 0 if self < 1
        #
        #     arr[self-1] ||= (self-1).fibonacci(arr)
        #     arr[self-2] ||= (self-2).fibonacci(arr)
        #
        #     self < 3 ? 1 : arr[self-1] + arr[self-2]
    end
end


# class Integer
#     # @@fibs = {}
#
#     def fibonacci
#         return 0 if self < 1
#         self < 3 ? 1 : (self-1).fibonacci + (self-2).fibonacci
#     end
# end


start_time = Time.now
puts 10000.fibonacci
stop_time = Time.now
puts (stop_time-start_time) * 1000