[LeetCode]Swap Nodes in Pairs

题目描述

Given a linked list, swap every two adjacent nodes and return its head.

For example,
Given 1->2->3->4, you should return the list as 2->1->4->3.

Your algorithm should use only constant space. You may not modify the values in the list, only nodes itself can be changed.

给你一个链表，交换相邻的两个链表

解题思路

1. 交换相邻两个链表节点，并将交换的尾节点记录；
2. 将上次的尾节点指向本次交换后的头节点；
3. 重复上述步骤；

以上需要注意如果节点个数为奇数的情况。

代码

public ListNode swapPairs(ListNode head) {ListNode node = head, result = head;ListNode firstNode = head;ListNode secondNode = head;ListNode lastNode = head;while (node != null) {firstNode = node;secondNode = node.next;if (secondNode == null) {//考虑节点个数为奇数的情况secondNode = node;} else {firstNode.next = secondNode.next;secondNode.next = firstNode;}if (firstNode == head) {//第一次交换时，记录最终交换完的头节点result = secondNode;} else {//上一次交换的尾节点指向本次交换完的头节点lastNode.next = secondNode;}lastNode = firstNode;node = firstNode.next;}return result;}