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?

Have you met this question in a real interview? 

Yes

Example

Given an example n=3 , 1+1+1=2+1=1+2=3

return 3

public class Solution {
    /**
     * @param n: An integer
     * @return: An integer
     */
    public int climbStairs(int n) {
        // write your code here
        if(n <= 1) return n;
        if(n == 2) return 2;
        int last = 1, lastLast = 1;
        int now = 0;
        for(int i = 2; i <= n; i++){
            now = last + lastLast;
            lastLast = last;
            last = now;
        }
        return now;
    }
}