Remove Duplicates from Sorted List leetcode java

 1     public ListNode deleteDuplicates(ListNode head) {
 2         if(head == null || head.next == null)
 3             return head;
 4         
 5         ListNode ptr1 = head;
 6         ListNode ptr2 = head.next;
 7         
 8         while(ptr2!=null){
 9             if(ptr1.val == ptr2.val){
10                 ptr2 = ptr2.next;
11                 if(ptr2==null)
12                     ptr1.next = null;
13             }else{
14                 ptr1.next = ptr2;
15                 ptr1 = ptr1.next;
16                 ptr2 = ptr2.next;
17             }
18         }
19 
20         return head;
21     }