问题描述：

java：

/*** Definition for singly-linked list.* public class ListNode {*     int val;*     ListNode next;*     ListNode() {}*     ListNode(int val) { this.val = val; }*     ListNode(int val, ListNode next) { this.val = val; this.next = next; }* }*/
class Solution {public ListNode deleteDuplicates(ListNode head) {if(head == null){return head;}ListNode p = head;ListNode q = p.next;while(q != null){if(q.val == p.val){q = q.next;p.next = q;}else{q = q.next;p = p.next;}    }return head;}
}