[leetcode]70. Climbing Stairs

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

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?

Note: Given n will be a positive integer.

方法一：递归（超时）

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

方法二：动态规划

class Solution{public:    int climbStairs(int n)    {        vector<int> res(n+1,0);        res[0]=1;        res[1]=1;        for(int i=2;i<=n;i++)        {            res[i]=res[i-1]+res[i-2];        }        return res[n];    }};