70. 爬楼梯

1. 题目链接

2. 解题思路：递推公式就是F(n) = F(n - 2) + F(n - 2)

3. 代码

   class Solution:
       def climbStairs(self, n: int) -> int:
           # 递推公式就是F(n) = F(n - 1) + F(n - 2)
           if n == 1:
               return 1
           if n == 2:
               return 2
           a = 1
           b = 2
           for i in range(3, n + 1, 1):
               c = a + b
               a = b
               b = c
           return b