LeetCode--024--两两交换链表中的节点(java)

 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) { val = x; }
 7  * }
 8  */
 9 class Solution {
10     public ListNode swapPairs(ListNode head) {
11         if(head == null || head.next == null) return head;
12         ListNode dummy = new ListNode(-1);
13         ListNode l1 = dummy;
14         ListNode l2 = head;
15         ListNode nextStart;
16         while(l2 != null && l2.next != null){
17             nextStart = l2.next.next;
18             l1.next = l2.next;
19             l2.next.next = l2;
20             l2.next = nextStart;
21             l1 = l2;
22             l2 = l2.next;
23             
24         }
25         return dummy.next;
26         
27         
28     }
29 }