82. Remove Duplicates from Sorted List II

 1     public ListNode deleteDuplicates(ListNode head) {
 2         if(head == null) {
 3             return null;
 4         }
 5         ListNode dummy = new ListNode(-1);
 6         dummy.next = head;
 7         boolean dup = false;
 8         ListNode next = head;
 9         ListNode cur = head;
10         ListNode pre = dummy;
11         while(cur != null) {
12             next = cur.next;
13             while(next != null && next.val == cur.val) {
14                 next = next.next;
15                 dup = true;
16             }
17             if(dup) {
18                 pre.next = next;
19             } else {
20                 pre = cur;
21             }
22             dup = false;
23             cur = next;
24         }
25         return dummy.next;
26     }