Question

I have m sets, which can be stored using array, or arraylist. There are overlaps among these sets. I would like to combine these m sets into a single set, and those duplicate elements will only occupy one spot in the combined set. Which kind of data structure and operation should I use to construct the combined set.

Answer 1

This code will do it for you:

    Set set = new HashSet();
    ArrayList list = new ArrayList();
    ArrayList list2 = new ArrayList(); //etc
    Object[] array = new Object[]{};
    Object[] array2 = new Object[]{}; // etc
    set.addAll(list);
    set.addAll(list2);
    set.addAll(Arrays.asList(array));
    set.addAll(Arrays.asList(array2));
    // Call addAll as many times as you like

set now contains all unique values once each