10扩展. 青蛙跳台阶

• 斐波那契数列，本质上和生兔子的原理一样，都是f(n) = f(n-1) + f(n-2)

class Solution:
    def jumpFloor(self, number):
        # write code here
        if number == 1 :return 1
        if number == 2 :return 2
        if not number:return None
        j = 2
        nums1 = 1
        nums2 = 2
        while j < number:
            res = nums1 + nums2
            nums1 = nums2
            nums2 = res
            j += 1
        return res