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?

public class Solution {    public int climbStairs(int n) {        //f(n)=f(n-1)+f(n-2);DP                int f1=1;        int f2=2;        /*for(int i=3;i<=n;i=i+2){            f1=f1+f2;            f2=f1+f2;        }        if(n%2==0) return f2;        else return f1;*/        // 解法二：        if(n==1) return 1;        if(n==2) return 2;        for(int i=3;i<=n;i++){            int f3=f1+f2;            f1=f2;            f2=f3;                    }        return f2;    }}