易知 f(n)=f(n-1)+f(n-2)+……f(1)
f(n-1)=f(n-2)+……f(1)
两式相减得f(n)=2f(n-1)

# -*- coding:utf-8 -*-
class Solution:
    def jumpFloorII(self, number):
        # write code here
        n=1 
        for i in range(2,number+1):
            n=2*n
        return n