82. Remove Duplicates from Sorted List II 

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class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        ListNode dummyHead = new ListNode(-1, head);
        ListNode pre = dummyHead, curr = head;

        while (curr != null) {
            if (curr.next != null && curr.val == curr.next.val) {
                // 当前节点重复，需要删除值相同的节点
                int val = curr.val;
                while (curr != null && curr.val == val) {
                    curr = curr.next;
                }
                pre.next = curr;
            } else {
                pre = curr;
                curr = curr.next;
            }
        }

        return dummyHead.next;
    }
}

References

82. Remove Duplicates from Sorted List II