LeetCode-Remove Duplicates from Sorted List II

题目：https://oj.leetcode.com/problems/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.

源码：Java版本
算法分析：时间复杂度O(n)，空间复杂度O(1)

/**
 * 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(head==null) {
            return null;
        }
       
        ListNode newHead=new ListNode(0);
        ListNode pre=null,node=head,newNode=newHead;
        while(node!=null) {
            if((pre==null || (pre!=null && pre.val!=node.val))
                    && (node.next==null || (node.next!=null && node.val!=node.next.val))) {
                newNode.next=node;
                newNode=node;
            }
            pre=node;
            node=node.next;
        }
        newNode.next=null;
        return newHead.next;
    }
}