/**

 * 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 head;

        ListNode* start = new ListNode();

        start->next = head;

        ListNode* cur = head;

        ListNode* prev = start;

        while(cur){

            while(cur->next && cur->next->val == prev->next->val)

                cur = cur->next;

            if(prev->next == cur)

                prev = cur;

            else

                prev->next = cur->next;

            cur = cur->next;

        }

        return start->next;

    }

};