Climbing Stairs

public class Solution {
    public int climbStairs(int n) {
        int[] res  =new int[n+3]; // 因为如果n<3,至少希望把前三个位置做出来
        res[0] = 0; 
        res[1] =1;
        res[2] = 2;
        if(n<3) return res[n];
        for(int i=3;i<=n;i++){
            res[i] = res[i-1]+res[i-2];
        }
        return res[n];
    }
}