剑指offer57 删除链表中重复的结点

class Solution {
public:
    ListNode* deleteDuplication(ListNode* pHead)
    {
        if(!pHead)
            return pHead;
        struct ListNode *pre=(struct ListNode *)malloc(sizeof(struct ListNode));
        pre->next=pHead;
        ListNode *p1=pre;
        ListNode *p2=pre->next;
        while(p2&&p2->next)
        {
            if(p2->val==p2->next->val)
            {
                p2=p2->next;
                while(p2->next&&p2->val==p2->next->val)
                {
                    p2=p2->next;
                }
                p1->next=p2->next;
                p2=p2->next;
            }
            else
            {
                p1=p1->next;
                p2=p2->next;
            }
        }
        return pre->next;
    }
};