删除排序链表中的重复元素 II

给定一个排序链表，删除所有含有重复数字的节点，只保留原始链表中 没有重复出现 的数字。

示例 1:

输入: 1->2->3->3->4->4->5
输出: 1->2->5
示例 2:

输入: 1->1->1->2->3
输出: 2->3

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }
        ListNode d = new ListNode(0);
        d.next = head;
        ListNode pre = d;
        while (head != null) {
            if (head.next != null && head.val == head.next.val) {
                while (head.next != null && head.val == head.next.val) {
                    head = head.next;
                }
                pre.next = head.next;
            }else {
                pre = head;
                
            }
            head = head.next;
        }
        return d.next;
    }
}