同普通青蛙跳一样用归纳法

# -*- coding:utf-8 -*-
class Solution:
    def jumpFloorII(self, number):
        # write code here
        if number <= 0:
            return 0
        elif number  ==1:
            return 1
        elif number == 2:
            return 2
        else:
            result = 2**(number-1)
            return result