/**
 * Definition of ListNode
 * class ListNode {
 * public:
 *     int val;
 *     ListNode *next;
 *     ListNode(int val) {
 *         this->val = val;
 *         this->next = NULL;
 *     }
 * }
 */


class Solution {
public:
    /*
     * @param head: head is the head of the linked list
     * @return: head of linked list
     */
    ListNode * deleteDuplicates(ListNode * head) {
        // write your code here
        if(head==NULL)
            return 0;
        ListNode *p=head;
        ListNode *next;
        while(p->next!=NULL)
        {
            next=p->next;
            if(next->val==p->val)
            {
                p->next=next->next;
                delete(next);
            }else//else很重要
            {
                p=p->next;
            }
            
        }
        return head;
    }
};