文章--LeetCode算法--ReverseNodesink-Group

目录

• ReverseNodesink-Group
  • 问题描述
  • 实例
  • 实现代码

ReverseNodesink-Group

问题描述

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 leftout nodes in the end should remain as it is.
You may not alter the values in the nodes, only nodes itself may be changed.
Only constant memory is allowed

实例

For 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

实现代码

    public class Solution {
        public ListNode reverseKGroup(ListNode head, int k) {
            if (head == null || head.next == null || k < 2)
                return head;
            ListNode dummy = new ListNode(0);
            dummy.next = head;
            ListNode tail = dummy, prev = dummy, temp;
            int count;
            while (true) {
                count = k;
                while (count > 0 && tail != null) {
                    count--;
                    tail = tail.next;
                }
                if (tail == null)
                    break;
                head = prev.next;
                while (prev.next != tail) {
                    temp = prev.next;// Assign
                    prev.next = temp.next;// Delete
                    tail.next = temp;// Insert
                }
                tail = head;
                prev = head;
            }
            return dummy.next;
        }
    }