70. 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.

Example 1:

Input: 2
Output: 2
Explanation: There are two ways to climb to the top.
1. 1 step + 1 step
2. 2 steps

Example 2:

Input: 3
Output: 3
Explanation: There are three ways to climb to the top.
1. 1 step + 1 step + 1 step
2. 1 step + 2 steps
3. 2 steps + 1 step

my code:

class Solution {
public:
    int climbStairs(int n) {
        vector<int> res(n+3, 0);
        for (int i = 0; i < n-1; ++i) {
            res[i+1] += res[i] + 1;
            res[i+2] += res[i] + 1;
        }
        return res[n];
    }
};

Runtime: 0 ms, faster than 100.00% of C++ online submissions for Climbing Stairs.