「LeetCode」24. 两两交换链表中的节点

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode swapPairs(ListNode head) {
        ListNode hair = new ListNode(-1,head);
        ListNode pre = hair;
        while (pre.next != null && pre.next.next != null) {
            ListNode one =pre.next;
            ListNode two =pre.next.next;
            one.next = two.next;
            two.next = one;
            pre.next = two;
            pre = one;
        }
        return hair.next;
    }
}