LeetCode_Climbing Stairs

ou 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?

分析：类似斐波那契序列，使用动态规划的思想。定义f(n)为台阶数为n时青蛙跳到台阶顶部的方法数。那么当n>2 时f(n) = f(n-1) + f(n-2)    f(1) = 1; f(2) = 2;

class Solution {
public:
    int climbStairs(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(n <= 2) return n;
        int f1 = 1, f2 = 2, res = 0;
        for(int i = 3; i <= n; ++i){
            res = f1 + f2;
            f1  = f2;
            f2  = res;
        }
        return res;
    }
};