LeetCode-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:

Code:

<span style="font-size:12px;">class Solution {public:    int climbStairs(int n) {        if (n == 0 || n == 1 || n == 2) return n;        int first = 1, second = 2, third;        for (int i = 3; i <= n; i++) {            third = first+second;            first = second;            second = third;        }        return third;    }};</span>