LeetCode70. 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?

Note: Given n will be a positive integer.

class Solution {public:    int climbStairs(int n) {        if(n==1) return 1;        if(n==2) return 2;        int i=3,res=3,imax=n+1,t1=1,t2=2;        while(i<imax){           res=t1+t2;           t1=t2;           t2=res;           ++i;        }        return res;    }};