Climbing Stairs

c++

class Solution {public:    int climbStairs(int n) {        if (n <= 0) return 0;        if (n == 1) return 1;        if (n == 2) return 2;        int pre_2 = 1;        int pre_1 = 2;        int cur = 0;        for (int i = 3; i <= n; ++i) {            cur = pre_1 + pre_2;            pre_2 = pre_1;            pre_1 = cur;        }        return cur;    }};

python

class Solution(object):    def climbStairs(self, n):        """        :type n: int        :rtype: int        """        if n<=0: return 0        if n==1: return 1        if n==2: return 2        pre_1, pre_2 = 2, 1        cur = 0        for i in xrange(3,n+1,1):            cur = pre_1 + pre_2            pre_2, pre_1 = pre_1, cur        return cur

reference:
https://leetcode.com/discuss/16866/basically-its-a-fibonacci