Remove Duplicates from Sorted List II

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

Code:

ListNode *deleteDuplicatesII(ListNode *head) {

    if (head==NULL || head->next==NULL)

        return head;

    ListNode *first = new ListNode(10);

    first->next = head;

    head = first;

    ListNode * pre = head;

    ListNode * cur = head;

    while(cur && cur->next)

    {

        if (cur->val == cur->next->val)

        {

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

            {

                ListNode * tmp  = cur->next;

                delete cur;

                cur = tmp;

            }

            pre->next = cur->next;

            delete cur;

            cur = pre->next;

        }

        else

        {

            pre = cur;

            cur = cur->next;

        }

    }

    ListNode *tmp = head->next;

    delete head;

    head = tmp;

    return head;

}