UnionFind

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;


public class UnionFind {

    Map<Integer, Integer> map = new HashMap<Integer, Integer>();

    UnionFind(HashSet<Integer> set) {
        for (Integer i : set) {
            map.put(i, i);
        }
    }

    UnionFind(int[] array) {
        for (int i = 0; i < array.length; i++) {
            map.put(array[i], array[i]);
        }

    }

    UnionFind(ArrayList<Integer> array) {
        for (Integer i : array) {
            map.put(i, i);
        }
    }

    public int find(int x) {
        int parent = map.get(x);
        while (parent != map.get(parent)) {
            parent = map.get(parent);
        }

        int father = map.get(x);
        while (father != map.get(father)) {
            int temp = map.get(father);
            map.put(father, parent);
            father = temp;
        }

        return parent;
    }

    public void union(int x, int y) {
        int root_x = find(x);
        int root_y = find(y);
        if (root_x != root_y) {
            map.put(root_x, root_y);
        }
    }

    public boolean connected(int p, int q) {
        return find(p) == find(q);
    }

}

Generic

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;



public class UnionFind<Item> {

    Map<Item, Item> map = new HashMap<Item, Item>();

    UnionFind(HashSet<Item> set) {
        for (Item i : set) {
            map.put(i, i);
        }
    }

    UnionFind(Item[] array) {
        for (int i = 0; i < array.length; i++) {
            map.put(array[i], array[i]);
        }
    }

    UnionFind(ArrayList<Item> array) {
        for (Item i : array) {
            map.put(i, i);
        }
    }

    public Item find(Item x) {
        Item parent = map.get(x);
        while (parent != map.get(parent)) {
            parent = map.get(parent);
        }

        Item father = map.get(x);
        while (father != map.get(father)) {
            Item temp = map.get(father);
            map.put(father, parent);
            father = temp;
        }

        return parent;
    }

    public void union(Item x, Item y) {
        Item root_x = find(x);
        Item root_y = find(y);
        if (root_x != root_y) {
            map.put(root_x, root_y);
        }
    }

    public boolean connected(Item p, Item q) {
        return find(p) == find(q);
    }
}