关于删除链表重复节点的问题

Question

关于删除链表重复节点的一道题目，不知道是哪里的逻辑错误,又要如何修改呢

```java
public ListNode deleteDuplicates(ListNode head) {
        if(head==null||head.next==null)
        return head;
        ListNode s=new ListNode(-1,head);
        ListNode pre=s;//让pre与nextNode间隔一个节点
        ListNode nextNode=head.next;
        while(nextNode!=null){
            if(pre.next.val==nextNode.val){
                while(pre.next.val!=nextNode.val){
                nextNode=nextNode.next;
            }
            pre.next=nextNode;
            }
            else{
                pre=pre.next;
                nextNode=nextNode.next;
            }
        }
        return s.next;
    }

```

Answer 1

public ListNode deleteDuplicates(ListNode head) {
    if (head == null || head.next == null) {
        return head;
    }
    ListNode s = new ListNode(-1, head);
    ListNode pre = s; // 让pre与nextNode间隔一个节点
    ListNode nextNode = head.next;
    while (nextNode != null) {
        if (pre.next.val == nextNode.val) {
            while (nextNode != null && pre.next.val == nextNode.val) {
                nextNode = nextNode.next;
            }
            pre.next = nextNode;
        } else {
            pre = pre.next;
        }
        if (nextNode != null) {
            nextNode = nextNode.next;
        }
    }
    return s.next;
}