#include <iostream>

using namespace std;

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 dummy(INT_MIN);

        dummy.next = head;

        ListNode *prev = &dummy,*cur = head;

        while(cur!= NULL)

        {

            bool duplicated = false;

            while(cur->next != NULL && cur->val == cur->next->val)

            {

                duplicated = true;

                cur = cur->next;

            }

            if(duplicated)

            {

                cur = cur->next;

                continue;

            }

            prev->next = cur;

            prev = prev->next;

            cur = cur->next;

        }

        prev->next = cur;

        return dummy.next;

    }

};

int main()

{

    ListNode *n1 = new ListNode();

    ListNode *n2 = new ListNode();

    ListNode *n3 = new ListNode();

    ListNode *n4 = new ListNode();

    ListNode *n5 = new ListNode();

    ListNode *n6 = new ListNode();

    ListNode *n7 = new ListNode();

    n1->next = n2;

    n2->next = n3;

    n3->next = n4;

    n4->next = n5;

    n5->next = n6;

    n6->next = n7;

    ListNode *ans;

    Solution myS;

    ans = myS.deleteDuplicates(n1);

    return ;

}