题解 | #删除有序链表中重复的元素-II#

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 dummy = new ListNode(-1), cur = dummy;
        dummy.next = head;

        while (cur != null) {
            ListNode next = cur.next;
            if (next == null) {
                break;
            }

            ListNode nextNext = next.next;
            if (nextNext == null || nextNext.val != next.val) {
                cur = next;
            } else {
                nextNext = nextNext.next;
                while (nextNext != null && nextNext.val == next.val) {
                    nextNext = nextNext.next;
                }
                cur.next = nextNext;
            }
        }

        return dummy.next;
    }
}

不过，官方答案貌似更简单了：
import java.util.*;
public class Solution {
    public ListNode deleteDuplicates (ListNode head) {
        //空链表
        if(head == null) 
            return null;
        ListNode res = new ListNode(0);
        //在链表前加一个表头
        res.next = head; 
        ListNode cur = res;
        while(cur.next != null && cur.next.next != null){ 
            //遇到相邻两个节点值相同
            if(cur.next.val == cur.next.next.val){ 
                int temp = cur.next.val;
                //将所有相同的都跳过
                while (cur.next != null && cur.next.val == temp) 
                    cur.next = cur.next.next;
            }
            else 
                cur = cur.next;
        }
        //返回时去掉表头
        return res.next; 
    }
}