/**

 * Definition for singly-linked list.

 * struct ListNode {

 *     int val;

 *     ListNode *next;

 *     ListNode(int x) : val(x), next(NULL) {}

 * };

 */

class Solution {

public:

    ListNode *deleteDuplicates(ListNode *head) {

        if (head == NULL) return NULL;

        ListNode *pp = head;

        ListNode *p = head->next;

        while (p != NULL)

        {

            if (p->val == pp->val)

            {

                pp->next = p->next;

                delete p;

                p = pp->next;

                continue;

            }

            pp = p;

            p = p->next;

        };

        return head;

    }

};