Leetcode 70 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?

Solution 1: simple DP

 public class Solution {  
   public int climbStairs(int n) {  
     if (n<=0) return 0;  
     int pre=0, res=1;  
     for (int i=1; i<=n; i++) {  
       int temp=res;  
       res=res+pre;  
       pre=temp;  
     }  
     return res;  
   }  
 }