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?

Analysis:

d[i] = d[i-1]+d[i-2]. i steps is the way of reaching i-1 steps + the way of reaching i-2 steps.

Solution:

public class Solution {
    public int climbStairs(int n) {
        if (n==0) return 0;
        if (n==1) return 1;
        if (n==2) return 2;
    
        int first = 1;
        int second = 2;
        for (int i=3;i<=n;i++){
            int newVal = first+second;
            first=second;
            second = newVal;
        }

        return second;
        
    }
}