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

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* p=head,*q=head;
        while(p->next)
        {
            if(p->next->val!=p->val)
            {
                q->next=p->next;
                q=q->next;
            }
            p=p->next;
        }
        q->next=NULL;
        return head;
    }
};