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 == 0) return 0;

        

        if (n == 1) return 1;

        

        // dp space complexity is O(n)

        vector<int> dp(n);

        dp[0] = 1;

        dp[1] = 2;

        

        for(int i = 2; i<n; i++)

        {

            dp[i] = dp[i-1] + dp[i-2];

        }

        

        return dp[n-1];

    }

};