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

链接：https://leetcode-cn.com/problems/remove-duplicates-from-sorted-list-ii

class Solution {
    public ListNode deleteDuplicates(ListNode head) {
         if(head ==null) return null;
         if(head.next==null) return head;
         ListNode s=new ListNode(0) ; //哨兵
         s.next = head;
         ListNode pre =s;
         ListNode curr =head;
         ListNode tmp =curr.next;
         if(tmp.next ==null ) {
             if(curr.val==tmp.val) {
                 return null; 
             }else {
                 return head;
             }
             
         }
         while(curr!=null) {
             while(tmp!=null&&curr.val!=tmp.val) {
                 pre =pre.next;
                 curr=curr.next;
                 tmp=tmp.next;
             }
             if(tmp==null) break;
             if(tmp.next ==null) {
                 pre.next=tmp.next;
                 return s.next;
             }
             while(tmp.next!=null&&tmp.val==tmp.next.val) {
                 tmp=tmp.next;
             }
             pre.next=tmp.next;
             curr =tmp.next;
             if(curr!=null) {
                 tmp=curr.next;
             }
             if(tmp==null) break;
             
         }    
        return s.next;
    }
}