[leetcode:python]70.Climing Stairs

题目：
You are climbing a stair case. It takes n steps to reach to the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

Note: Given n will be a positive integer.
斐波那契数列的变形题

方法一：性能39ms

class Solution(object):
    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        dp = [1 for i in range(n + 1)]
        for i in range(2, n + 1):
            dp[i] = dp[i-1] + dp[i-2]
        return dp[n]

方法二：性能32ms

class Solution(object):
    def climbStairs(self, n):
        """
        :type n: int
        :rtype: int
        """
        a = b = 1
        for i in range(n-1):
            a, b = a + b, a

        return a

这个方法的时间复杂度和空间复杂度都大大减小了耶。