/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode deleteDuplication(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }

        ListNode next = head.next;
        if (head.val == next.val) {
            while(next != null && head.val ==next.val) {
                next = next.next;
            }
            return deleteDuplication(next);
        } else {
            head.next = deleteDuplication(head.next);
            return head;
        }
    }
}