Leetcode24--->Swap Nodes in Pairs(交换单链表中相邻的两个节点)

 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 public class Solution {
10     public ListNode swapPairs(ListNode head) {
11         if(head == null)
12             return head;
13         ListNode cur = head;
14         ListNode prev = cur;  // 连接每对节点
15         if(cur.next != null)
16             head = cur.next;
17         while(cur != null && cur.next != null){
18             prev.next = cur.next;
19             ListNode next = cur.next.next;  // next用来保存下一对节点的开始节点
20             cur.next.next = cur;
21             cur.next = next;  
22             prev = cur;  // prev指向每一对反转之后节点的第二个节点
23             cur = next;  // cur指向每一对节点的第一个节点
24         }
25         return head;
26     }
27 }