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?

这题如果用递归, 超时了, 只能模拟了

class Solution {
public:
    int climbStairs(int n) {
        if(n==0)return 0;
        if(n==1)return 1;
        if(n==2)return 2;
        int be  = 1;
        int aft = 2;
        int i;
        int sums;
        for(i=3;i<=n;i++)
        {
            sums = aft + be;
            be   = aft;
            aft  = sums;
        }
        return sums;
    }
};