Remove Duplicates from Sorted List II

Remove Duplicates from Sorted List II 

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if(null == head || null == head.next)        //只有1个节点或者空时，直接返回头结点
            return head;
        ListNode temp = new ListNode(0);
        temp.next = head;
        head = temp;//加一个头结点，不放内容
        
        ListNode pre = head;
        ListNode behind = head.next;
        ListNode front = behind.next;
        
        while(null != front){
            if(behind.val == front.val){            //如果有相同的，删除掉
                while(null != front && behind.val == front.val)
                    front = front.next;
                if(null == front)
                    pre.next = null;
                else{
                    pre.next = front;
                    behind = front;
                    front = front.next;
                    continue;
                }
            }
            if(null != front){
                front = front.next;
                behind = behind.next;
                pre = pre.next;
            }
        }
        return head.next;
    }
}