删除排序链表中的重复元素

class Solution {

public:

    ListNode* deleteDuplicates(ListNode* head) {

        ListNode* newhead =new ListNode(-1,head);

        ListNode* p = newhead;

        while(p->next&&p->next->next){

            if(p->next->val==p->next->next->val){

                int val = p->next->val;

                while(val==p->next->val){

                    p->next = p->next->next;

                    if(p->next==nullptr)

                     return newhead->next;

                }

            }

            else{

                p = p->next;

            }

        }

        return newhead->next;

    }

};