class Solution 
{
public:
    //递归方法：在LeetCode测试，发现超时
    int climbStairs_recur(int n)
    {
        if (1 == n)
        {
            return  1;
        }
        else if (2 == n)
        {
            return 2;
        }
        else
        {
            return climbStairs_recur(n-2) + climbStairs_recur(n-1);
        }
    }
    //循环方法：利用了上一次的计算结果，速度快
    int climbStairs_loop(int n)
    {
        if (1 == n)
        {
            return  1;
        }
        else if (2 == n)
        {
            return 2;
        }

        int cur = 2;
        int last = 1;
        for (int i=3; i<=n; i++)
        {
            int t =  last + cur;
            last = cur;
            cur = t;
        }
        return cur;        
    }
};