删除排序链表中的重复元素 II

class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        // 创建哑节点，方便处理头节点可能被删除的情况
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        
        // prev指向当前确定不重复的节点
        ListNode prev = dummy;
        
        // curr遍历链表
        ListNode curr = head;
        
        while (curr != null) {
            // 检查当前节点是否有重复
            boolean isDuplicate = false;
            while (curr.next != null && curr.val == curr.next.val) {
                isDuplicate = true;
                curr = curr.next;
            }
            
            if (isDuplicate) {
                // 如果有重复，跳过所有重复节点
                prev.next = curr.next;
            } else {
                // 如果没有重复，prev移动到当前节点
                prev = prev.next;
            }
            
            // curr继续前进
            curr = curr.next;
        }
        
        return dummy.next;
    }
}