/**

 * Definition of ListNode

 * class ListNode {

 * public:

 *     int val;

 *     ListNode *next;

 *     ListNode(int val) {

 *         this->val = val;

 *         this->next = NULL;

 *     }

 * }

 */

class Solution {

public:

    /**

     * @param head: The first node of linked list.

     * @return: head node

     */

    ListNode *deleteDuplicates(ListNode *head) {

        // write your code here

        if(head==NULL)

        return 0;

        if(head->next==NULL)

        return head;

        ListNode *cur=head;

        ListNode *pre=NULL;

        while(cur!=NULL)

        {

            if(pre!=NULL&&pre->val==cur->val)

            {

                pre->next=cur->next;

                cur=pre->next;

            }

            else

            {

                pre=cur;

                cur=pre->next;

            }

        }

        return head;

    }

};