Question：

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，一次只能爬1阶或者2阶，问总共有多少种结果。

Algorithm：

Dynamic Programming动态规划，s[i]=s[i-1]+s[i-2]

Accepted Code:

class Solution {
public:
    int climbStairs(int n) {
        if(n==0)return 0;
        else if(n==1)return 1;
        else if(n==2)return 2;
        vector<int> res(n,0);
        res[0]=1;
        res[1]=2;
        for(int i=2;i<n;i++)
            res[i]=res[i-1]+res[i-2];
        return res[n-1];
    }
};