题目
给你一个链表,两两交换其中相邻的节点,并返回交换后链表的头节点。你必须在不修改节点内部的值的情况下完成本题(即,只能进行节点交换)。
示例 1:
输入:head = [1,2,3,4]
输出:[2,1,4,3]
解
class Solution {public ListNode swapPairs(ListNode head) {if(head == null || head.next == null){return head;}ListNode dummy = new ListNode(0);dummy.next = head;ListNode pre = dummy;ListNode cur = head;ListNode next = null;while (cur != null) {next = cur.next;ListNode p1 = null;if (next != null) {p1 = next.next;next.next = cur;pre.next = next;cur.next = p1;}else{pre.next = cur;}pre = cur;cur = p1;}return dummy.next;}
}