Leetcode Climbing Stairs

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?

爬楼梯问题，每一次可以爬1阶或者2阶，问爬上N阶的选择法，爬上1阶的选择1种，爬上2阶的选择有2种，

爬上N阶的选择有f(N) = f(N-1)+f(N-2).....

当使用递归算法的时候会超时！！！！！！

class Solution {public:    int climbStairs(int n) {        if(n==1)            return 1;        if(n==2)            return 2;        return climbStairs(n-1)+climbStairs(n-2);    }};

Submission Result: Time Limit Exceeded

改进方法后.......

class Solution {public:    int climbStairs(int n) {        int result,s1=1,s2=2;        if(n==1)            return s1;        if(n==2)            return s2;        for(int i=3;i<=n;i++)        {            result = s1 + s2;            s1 = s2;            s2 = result;        }        return result;    }};

Submission Result: Accepted