leetcode: (70) Climbing Stairs

【Question】

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?

可以发现规律nums
=nums[n-1]+nums[n-2];

 可以用递归和非递归，使用递归时复杂度较高

下面给出非递归

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