leetcode 82 Remove Duplicates from Sorted List II C++

这道题题意很简单，但是容易出错，特别是第一个Node需要删掉的情况，所以可以使用一个dumyNode来做，简单而且不容易出错。

    ListNode* deleteDuplicates(ListNode* head) {
        if (!head || !head->next) return head;
        ListNode *dummy = new ListNode(0);
        dummy->next = head;
        head = dummy;
        while(head->next && head -> next -> next) {
            if(head->next->val == head->next->next->val) {
                int val = head->next->val;
                while(head->next && head->next->val == val) {
                    head->next = head->next->next;
                }
            } else {
                head = head->next;
            }
        }
        return dummy->next;
    }