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:
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。
参考代码
package leetcode
// ListNode define
type ListNode = structures.ListNode
/**
* Definition for singly-linked list.
* type ListNode struct {
* Val int
* Next *ListNode
* }
*/
func reverseKGroup(head *ListNode, k int) *ListNode {
node := head
for i := 0; i < k; i++ {
if node == nil {
return head
}
node = node.Next
}
newHead := reverse(head, node)
head.Next = reverseKGroup(node, k)
return newHead
}
func reverse(first *ListNode, last *ListNode) *ListNode {
prev := last
for first != last {
tmp := first.Next
first.Next = prev
prev = first
first = tmp
}
return prev
}