How to write a method that recieves an ADT and removes duplicates?

Question

We are given an implementation of the genericSackADT (code below) that implements the iterable interface.

public interface GSackIterableADT<T> extends Iterable<T> {
        void add(T item);
        T remove() throws NoSuchElementException;
        boolean isEmpty();
        Iterator<T> iterator();

We are supposed to write a method that can accept this as input and remove all duplicates.

I think I need some conceptual guidance on this. My plan right now is to create a method called removeDuplicates that uses an iterator to scan through the ADT and remove duplicates when they are found. I checked the iterator API and I should be able to use E next () and void remove () to do this, correct? However, my code is a mess right now and I'm not sure where exactly to go...

public static <E> int removeDuplicates (match) {
        int counter = 0;
        ListIterator<E> iter = myList.listiterator();
        while (iter.hasNext());
        E val = iter.next();
        //the goal in the next step is to remove duplicates as the iterator finds them
        if (val.equals(match){
            void remove()

Answer 1

One easy way to remove duplicates is to add your collection to a Set, and then convert it back to a List. The Java Set implementations will automatically remove duplicates during an add() operation. I assume your implementation is using a List under the hood telling from your sample code.

public static List<E> removeDuplicates (List<E> inputList) {
    int dupCount = 0;
    Set<E> listSet = new HashSet<E>();
    ListIterator<E> iter = inputList.listIterator();
    while (iter.hasNext()) {
        E val = iter.next();
        if (!listSet.add(val)) {
            ++dupCount;
        }
    }

    // you can log the number of duplicates if you want

    List<E> newList = Arrays.asList(listSet.toArray());

    return newList;
}