Climbing Stairs

class Solution {public:    int climbStairs(int n) {        //其实是斐波那契数列的变形问题，f(n) = f(n-1) + f(n-2)        int last1 = 1, last2 = 1;//f0 = 1, f1 = 1        int result = 1;        for(int i = 2;i<=n;i++)        {            result = last1 + last2;            last1 = last2;            last2 = result;        }                return result;    }};