leetcode Climbing Stairs

class Solution {public:    int climbStairs(int n) {        if(n == 0) return 0;        if(n == 1) return 1;        if(n == 2) return 2;                int prepre = 1;         int pre = 2;        int cur = 0;        for(int i = 3;i <= n;i ++) {        cur = prepre + pre;        prepre = pre;        pre = cur;}return cur;            }};