归纳法：
第一步：第一行是number值，第二行是步数，归纳完就是f(n) = f(n-1) + f(n-2)
第二步：找循环，number = 3，需要循环1次。number = 4，需要循环2次... ...
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1 2 3 5 8 13 21

# -*- coding:utf-8 -*-
class Solution:
    def jumpFloor(self, number):
        # write code here
        if number <= 0 : 
            return 0
        elif number == 1:
            return 1
        elif number == 2:
            return 2
        else:
            a = 1
            b = 2
            i = 0
            while i <= number-3:
                i+=1
                a, b = b, a+b
            return b