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?

Solution:

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