leetcode

class :
    def climbStairs(self, n: int) -> int:
        if (n == 1):
            return 1
        elif (n == 2):
            return 2
        else:
            res = [0] * (n+1)
            res[1] = 1
            res[2] = 2
            for i in range(3, n+1):
                res[i] = res[i-1] + res[i-2]
            return res[n]