爬楼梯

题源：leetcode

链接：https://leetcode-cn.com/problems/climbing-stairs/

 这也是道简单的动态规划题，状态转移方程为：f(x) = f(x-1)+f(x-2)

class Solution {
public:
    int climbStairs(int n) {
        int p = 0;
        int q = 0;
        int r = 1;

        for(int i = 0; i < n; i++){
            p = q;
            q = r;
            r = p+q;
        }
        return r;
    }
};