LeetCode(70)-Climbing Stairs

版权声明：XiangYida https://blog.csdn.net/qq_36781505/article/details/83722413

70-Climbing Stairs

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 step + 1 step
2 steps
Example 2:
Input: 3
Output: 3
Explanation: There are three ways to climb to the top.
1 step + 1 step + 1 step
1 step + 2 steps
2 steps + 1 step

题目的意思是爬楼梯，每次爬的时候可以选择爬2阶或者一阶，然后给你n阶台阶，问你有多少种爬上去的可能

嗯？这个题没有找到思路还真的不好做，典型的动态规划（嗯，虽然还没搞懂动态规划）
怎么说呢，找出局部能替代整体的部分，相当于递推吧。

比如这个题，你要爬到第i阶，那么有两种可能，第一种你是从i-1阶跳一阶跳上来的，第二种，你是从i-2阶跳2阶跳上来的，所以第i阶的种数=（i-1)的种数+（i-2)的种数，然后代码就是这样了，也就几行。（好懒，好几天没做题了）

public int climbStairs(int n) {
       int a1=1;
       int a2=2;
       int a3=0;
       if(n==1||n==2)return n;
       for(int i=3;i<=n;i++){
           a3=a2+a1;
           a1=a2;
           a2=a3;
       }
       return a3;
   }