Remove Duplicates from Sorted List II

 1 public class Solution {
 2     public ListNode deleteDuplicates(ListNode head) {
 3         if(head==null || head.next==null)
 4             return head;
 5         ListNode safe = new ListNode(-1);
 6         ListNode pre = head;
 7         ListNode cur = safe;
 8         while(pre!=null){
 9             boolean dul = false;
10             while(pre.next!=null && pre.val == pre.next.val){
11                 pre = pre.next;
12                 dul = true;
13             }
14             if(dul){
15                 pre = pre.next;
16                 continue;
17             }
18             cur.next = pre;
19             pre = pre.next;
20             cur = cur.next;
21         }
22         cur.next = null; //because {1,1}
23         return safe.next;
24     }
25 }