82. Remove Duplicates from Sorted List II

public static ListNode deleteDuplicates(ListNode head) {        if(head == null || (head != null && head.next == null)){            return head;        }        ListNode cur = head.next, thead = head, tcur = head,pre = null;         boolean isDu = false;        while(cur != null) {            if(cur.val == tcur.val) {                isDu = true;            }else if(cur.val != tcur.val && isDu) {                if(pre == null) {                    thead = cur;                    tcur = cur;                }else {                    pre.next = cur;                    tcur = cur;                }                isDu = false;            }else if(cur.val != tcur.val && !isDu) {                pre = tcur;                tcur.next = cur;                tcur = cur;            }             cur = cur.next;        }        if(isDu) {            if(pre == null) {                thead = null;            }else {                pre.next = null;            }        }else {            tcur.next = null;        }        return thead;    }