LeetCode() Remove duplicates from sorted list II

 ListNode* dummy = new ListNode(0); //必须要加上 new ListNode(0); 否则有错误。
        dummy->next = head;
        head = dummy;
        while(head->next && head->next->next) {
            if(head->next->val == head->next->next->val) {
                int value = head->next->val;
                while(head->next && head->next->val == value) {
                    head->next = head->next->next;
                }
            } else {
                head = head->next;
            }
        }
        return dummy->next;