# [25. Reverse Nodes in k-Group](https://leetcode.com/problems/reverse-nodes-in-k-group/description/)

## 题目

Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.

k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes in the end should remain as it is.

Example:

```c
Given this linked list: 1->2->3->4->5

For k = 2, you should return: 2->1->4->3->5

For k = 3, you should return: 3->2->1->4->5
```

Note:

- Only constant extra memory is allowed.
- You may not alter the values in the list's nodes, only nodes itself may be changed.


## 题目大意

按照每 K 个元素翻转的方式翻转链表。如果不满足 K 个元素的就不翻转。

## 解题思路


这一题是 problem 24 的加强版，problem 24 是两两相邻的元素，翻转链表。而 problem 25 要求的是 k 个相邻的元素，翻转链表，problem 相当于是 k = 2 的特殊情况。