题解 | #删除有序链表中重复的元素-II#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 */

#include <cstdio>
class Solution {
public:
    /**
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    ListNode* deleteDuplicates(ListNode* head) {
        // write code here
        if(head==NULL||head->next==NULL) return head;
        ListNode* dummy=new ListNode(1001);
        dummy->next=head;
        ListNode* p=head,*pre=dummy,*q=dummy;
        while(p->next)
        {
            if(p->next->val!=p->val&&p->val!=pre->val)
            {
                q->next=p;
                q=q->next;
            }
            pre=p;
            p=p->next;
        }
        if(p->val!=pre->val) 
        {
            q->next=p;
            q=q->next;   
        }
        q->next=NULL;
        return dummy->next;
    }
};