LeetCode : Swap Nodes in Pairs [java]

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.

思路：纯链表操作，使用额外节点记录"指针"，主要需要记录的是：当前交换的两个节点，两个节点后的节点（如果有的话）以及构建新链表的"指针".

/**
* Definition for singly-linked list.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode swapPairs(ListNode head) {
ListNode myHead = new ListNode(-1);
ListNode myPointer = myHead;
while (head != null) {
ListNode next2 = head.next;
if (next2 == null) {
myPointer.next = head;
break;
} else {
next2 = next2.next;
ListNode qian = head;
ListNode hou = head.next;
qian.next = hou.next;
hou.next = qian;
myPointer.next = hou;
myPointer = myPointer.next.next;
head = next2;
}
}
return myHead.next;
}
}