code.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        ListNode dummy = new ListNode(-1);
        dummy.next = head;
        ListNode ptr = dummy;
        while (ptr.next != null) {
            if (ptr.next.next != null && ptr.next.val == ptr.next.next.val) {
                int del = ptr.next.val;
                while (ptr.next != null && ptr.next.val == del) {
                    deleteNext(ptr);
                }
            } else {
                ptr = ptr.next;
            }
        }
        return dummy.next;
    }
    
    private void deleteNext(ListNode node) {
        node.next = node.next.next;
    }
}