題目：

我的解答：

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode swapPairs(ListNode head) {
        ListNode list1=new ListNode(0);
        list1.next=head;
        ListNode list2=list1;
        while(head!=null&&head.next!=null){
            list2.next=head.next;
            head.next=list2.next.next;
            list2.next.next=head;
            list2=list2.next.next;
            head=list2.next;
        }
        return list1.next;
        
    }
}