code: import java.util.*;
  
  public class SetConsolidation {
  
      public static void main(String[] args) {
          List<Set<Character>> h1 = hashSetList("AB", "CD");
          System.out.println(consolidate(h1));
  
          List<Set<Character>> h2 = hashSetList("AB", "BD");
          System.out.println(consolidateR(h2));
  
          List<Set<Character>> h3 = hashSetList("AB", "CD", "DB");
          System.out.println(consolidate(h3));
  
          List<Set<Character>> h4 = hashSetList("HIK", "AB", "CD", "DB", "FGH");
          System.out.println(consolidateR(h4));
      }
  
      // iterative
      private static <E> List<Set<E>>
                  consolidate(Collection<? extends Set<E>> sets) {
  	List<Set<E>> r = new ArrayList<>();
  	for (Set<E> s : sets) {
  	    List<Set<E>> new_r = new ArrayList<>();
  	    new_r.add(s);
  	    for (Set<E> x : r) {
  		if (!Collections.disjoint(s, x)) {
  		    s.addAll(x);
  		} else {
  		    new_r.add(x);
  		}
  	    }
  	    r = new_r;
  	}
  	return r;
      }
  
      // recursive
      private static <E> List<Set<E>> consolidateR(List<Set<E>> sets) {
          if (sets.size() < 2)
              return sets;
          List<Set<E>> r = new ArrayList<>();
          r.add(sets.get(0));
          for (Set<E> x : consolidateR(sets.subList(1, sets.size()))) {
              if (!Collections.disjoint(r.get(0), x)) {
                  r.get(0).addAll(x);
              } else {
                  r.add(x);
              }
          }
          return r;
      }
  
      private static List<Set<Character>> hashSetList(String... set) {
          List<Set<Character>> r = new ArrayList<>();
          for (int i = 0; i < set.length; i++) {
              r.add(new HashSet<Character>());
              for (int j = 0; j < set[i].length(); j++)
                  r.get(i).add(set[i].charAt(j));
          }
          return r;
      }
  }
  