Python, LintCode, 111. 爬樓梯

class Solution:
    """
    @param n: An integer
    @return: An integer
    """
    def climbStairs(self, n):
        # write your code here
        res = [0, 1, 2]
        if n <= 2:
            return res[n]
        for i in range(3, n+1):
            res.append(res[i-1] + res[i-2])
        return res[n]