leetcode 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?

1,注意函数  f（n）=f(n-1)+f(n-2)

 

package Leetcode;

public class ClimbingStairs {
    public int climbStairs(int n) {
        if(n<=1){
            return n;
        }
        int before=1;
        int beforebefore=1;
        int current=0;
        for(int i=2;i<=n;i++){
            current=before+beforebefore;
            beforebefore=before;
            before=current;
        }
        return current;
    }
}