刷题记录：70. 爬楼梯

70. 爬楼梯

class Solution:
    def climbStairs(self, n: int) -> int:
        if n <= 2:
            return n

        pre, cur = 1, 2

        for i in range(3,n+1):
            pre, cur = cur, pre + cur
        
        return cur