【剑指offer】13_矩形覆盖

class Solution:
    def rectCover(self, number):
        if number < 0:
            return None
        elif number == 1 or number == 2 or number == 0:
            return number
        else:
            first = 1
            second = 2
            for i in range(number - 2):
                num = first + second
                first = second
                second = num
            return num