迭代解法：

 

 

class Solution {public ListNode swapPairs(ListNode head) {ListNode dummyHead = new ListNode(0);dummyHead.next = head;ListNode temp = dummyHead;while (temp.next != null && temp.next.next != null) {ListNode node1 = temp.next;ListNode node2 = temp.next.next;temp.next = node2;node1.next = node2.next;node2.next = node1;temp = node1;}return dummyHead.next;}
}