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;

    }

};