Write the most efficient implementation of the function RemoveDuplication()

Question

so i am studying and i have this question , Write the most efficient implementation of the function RemoveDuplication(), which removes any duplication in the list. Assume that the list is sorted but may have duplication. So, if the list is originally 
<2, 2, 5, 6, 6, 6, 9>, your function should make it <2, 5, 6, 9>.

the code that i thought of to remove the duplication is this right here , i wanted to know , if there is more efficient ways of removing the duplications in the list

template <class T>
void DLList<T>:: RemoveDuplication()
{
    for(DLLNode<T>*ptr = head; ptr!=NULL; ptr=ptr->next)
        while (ptr->val == ptr->next->val)
        {
            ptr->next->next->prev = ptr;
            ptr->next = ptr->next->next;
        }
}

Answer 1

It looks like your code will run in O(n) which is good for an algorithm. It is probably not going to be any more efficient, because you'll have to visit every item to delete it.

If you don't want to delete duplicate objects though, but want to return an new list containing the non-duplicate objects, you could make it slightly faster by making it O(m) where m is the amount of unique numbers, which is smaller or equal to n. But i couldn't think up any way to do this.

Recapping, it is possible to be slightly faster, but this is hard and the improvement is negligible.

ps. Dont forget to delete stuff when you take it out of your list ;)