gistfile1.java

    @Override
    public boolean removeAll(Collection<?> c) {
        for(Object item: c) {
            int index = indexOf(item);
            while(index >= 0) {
                remove(index);
                index = indexOf(item);
            }
        }

        return true;
    }

    @Override
    public boolean retainAll(Collection<?> c) {
        Object[] arr = toArray();
        for(Object item: arr) {
            if(!c.contains(item)) {
                int index = indexOf(item);
                while(index >= 0) {
                    remove(index);
                    index = indexOf(item);
                }
            }
        }

        return true;
    }