[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?

其实想想就是一个斐波拉契数列，考虑:

s(n) = s(n-1) + s(n-2);

s(1) = 1;

s(2) = 2;

s(3)  = s(1) + s(2) = 3;

class Solution {
public:
    int climbStairs(int n) {
        if (n == 1)
            return 1;
        else if (n == 2)
            return 2;
        else
        {
            int first = 1;
            int second = 2;
            
            for (int i=2; i<n; i++)
            {
                int temp = second;
                second = first + second;
                first = temp;
            }
            return second;
        }
    }
};