leedcode 爬楼梯

斐波那契数列：

class Solution:
    def climbStairs(self, n: int) -> int:
        if n==1:
            return 1

        s=[0]*(n+1)

        s[1]=1
        s[2]=2


        for i in range(3,n+1):

            s[i]=s[i-1]+s[i-2]

        return s[n]