Leetcode 70. Climbing Stairs

题目链接：https://leetcode.com/problems/climbing-stairs/

题目描述：

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?

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思路：动态规划，找递推公式，爬到第n级楼梯总的方式：f(n)，要么从n-1级爬上来的，要么就是n-2级爬上来的，递推公式：f(n)=f(n-1)+f(n-2)

两种方法，循环和递归，递归超时（功能正确）

代码1：循环

class Solution {
public:
    int climbStairs(int n) {
        if(n==1||n==2)
            return n;
        int fn_1=2;
        int fn_2=1;
        int tmp;
        for(int i=3;i<=n;i++)
        {
            tmp=fn_1+fn_2;
            fn_2=fn_1;
            fn_1=tmp;
        }
        return tmp;
    }
};

代码2：递归

class Solution {
public:
    int climbStairs(int n) {
        return climb(n);
    }
    int climb(int n)
    {
        int re;
        if(n==1||n==2)
            return n;
        re=climb(n-1)+climb(n-2);
        return re;
    }
};