70. Climbing Stairs

Java

public class Solution {
    public int climbStairs(int n) {
        if(n==1) return 1;
        if(n==2) return 2;
        int result=0;
        int tmp1=1;
        int tmp2=2;
        for(int i=2;i<n;i++)
        {
            result=tmp1+tmp2;
            tmp1=tmp2;
            tmp2=result;
        }
        return result;
    }
}