剑指offer10.矩形覆盖

https://www.nowcoder.com/practice/72a5a919508a4251859fb2cfb987a0e6?tpId=13&tqId=11163&tPage=1&rp=1&ru=%2Fta%2Fcoding-interviews&qru=%2Fta%2Fcoding-interviews%2Fquestion-ranking

题目描述
我们可以用21的小矩形横着或者竖着去覆盖更大的矩形。请问用n个21的小矩形无重叠地覆盖一个2*n的大矩形，总共有多少种方法？

见leetcode70：

# -*- coding:utf-8 -*-
class Solution:
    def rectCover(self, number):
        # write code here
        if number <= 2:
            return number
        a, b = 1, 2
        while number > 2:
            a, b = b ,a+b
            number -= 1
        return b