70. Climbing Stairs 解题记录

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?

Note: Given n will be a positive integer.

Example 1:

Input: 2
Output:  2
Explanation:  There are two ways to climb to the top.

1. 1 step + 1 step
2. 2 steps

Example 2:

Input: 3
Output:  3
Explanation:  There are three ways to climb to the top.

1. 1 step + 1 step + 1 step
2. 1 step + 2 steps
3. 2 steps + 1 step

解题思路：

这道题由题意可以得到一个递推公式an=a(n-1)+a(n-2)，我一开始是用递归来写，可能是因为嵌套太多层的原因，超过了时限，然后换成了循环。

代码：

class Solution {
public:
    int climbStairs(int n) {
        int pre=1;
        int cur=1;
        for(int i=1;i<n;i++){
            int t=cur;
            cur=pre+cur;
            pre=t;
        }
        return cur;
    }
};