munnipea

Map<String, String> people;

    Map<String, Integer> rank;

    public DisjointSubsets() {
        people = new HashMap<>();
        rank = new HashMap<>();
    }

    public String find(String element) throws IllegalArgumentException {
        // TODO
        // should throw IllegalArgumentException if the element is not present
        if (element == null || element.equals("") || !people.containsKey(element)) {
            throw new IllegalArgumentException();
        }
        String firstParent = people.get(element);
        while (!people.get(firstParent).equals(firstParent)) {
            firstParent = people.get(firstParent);
        }

        return firstParent;
    }

    // should throw IllegalArgumentException if any of elements is not present
    public void union(String element1, String element2) throws IllegalArgumentException {
        // TODO
        // should throw IllegalArgumentException if any of elements is not present
        if (element1 == null || element2 == null || element2.equals("") || element1.equals("") || !people.containsKey(element2) || !people.containsKey(element1)) {
            throw new IllegalArgumentException();
        }
        String x = find(element1);
        String y = find(element2);

        if (find(element1).equals(element2)) {
            return;
        }
        if (rank.get(x) > rank.get(y))
            people.put(y, x);
        else if (rank.get(x) < rank.get(y))
            people.put(x, y);
        else {
            people.put(x, y);
            rank.put(y, rank.get(y) + 1);
        }

    }

    public void addSubset(String element) throws IllegalArgumentException {
        // TODO
        // should throw IllegalArgumentException if the element is already present
        if (element == null || element.equals("") || people.containsKey(element)) {
            throw new IllegalArgumentException();
        }
        people.put(element, element);
        rank.put(element, 0);

    }