class CustomList{
    TreeSet indexes;
    HahMap items;
    int maxSize = 0;
    int realSize = 0;
    add(Object item) {
        int curItemIndex = maxSize++;
        realSize ++;
        indexes.add(curItemIndex);
        items.put(curItemIndex, item);
    }
    remove(int index) {
        int realIndex = indexes.getByIndex(index);
        realSize--;
        indexes.remove(realIndex)
        item.remove(realIndex);
    }

    getByIndex(int index) {
		int realIndex = indexes.getByIndex(index);
 		return items.get(realIndex);
	}



}