70 Climbing Stairs

https://leetcode.com/problems/climbing-stairs/

solution

# 空间优化写法: 状态转移过程中只依赖过去两步
class Solution:
    def climbStairs(self, n: int) -> int:
        if n <= 2:
            return n
        prev = 1
        cur = 2
        for i in range(3, n + 1):
            dp = prev + cur
            prev = cur
            cur = dp
        return cur

时间复杂度：O(n) 空间复杂度：O(1)