https://oj.leetcode.com/problems/climbing-stairs/

Climbing Stairs.java

public class Solution {
    public int climbStairs(int n) {
        if (n == 0) return 0;
        if (n == 1) return 1;
        if (n == 2) return 2;
        int ret = 0;
        int tempa = 2;
        int tempb = 1;
        for (int i = 3; i <= n; i++){
            ret = tempa + tempb;
            tempb = tempa;
            tempa = ret;
        }
        return ret;
    }
}