Leetcode-Easy 70. Climbing Stairs

class Solution:
    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        # 递归 time limit
#         if n==1 or n==2:
#             return n
#         return Solution.climbStairs(self,n-1)+Solution.climbStairs(self,n-2)
        ## 备忘录算法 time limit
#         data={}
#         if n==1 or n==2:
#             return n
#         if n in data:
#             return data['n']
#         else:
#             value=Solution.climbStairs(self,n-1)+Solution.climbStairs(self,n-2)
#             data['n']=value
#             return value
        ## 动态规划
        if n==1 or n==2:
            return n
        first=1
        second=2
        temp=0
        for i in range(n-2):
            temp=first+second
            first=second
            second=temp
        return temp