import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode deleteDuplicates (ListNode head) {
        if(head == null){
            return head;
        }

        ListNode cur = head;
        while(cur != null){
            ListNode next = cur.next;
            while(next != null && next.val == cur.val){
                next = next.next;
            }

            cur.next = next;
            cur = cur.next;
        }

        return head;
    }
}