Leetcode70 suppose you are climbing stairs. You need n steps to reach the roof. You can climb one or two steps at a time. How many different ways can you climb to the roof?

class Solution {
public:
    int climbStairs(int n) {
        // 1  Initialize array 
        std::vector<int> f(n);

        // 2  Define boundary conditions 
        if (n == 1)
        {
            return 1;
        }
        if (n == 2)
        {
            return 2;
        }

        f[0] = 1;
        f[1] = 2;

        // 3  State transition equation 
        for (int i = 2; i < n; i++)
        {
            f[i] = f[i - 1] + f[i - 2];
        }

        // 4  Find out the results 
        return f[n-1];
    }
};