import java.util.*;

/**
 * This class was implemented to preserve 
 * MySQL functionality. MySQL does not support 
 * the use of subqueries in set operations, so
 * it was necessary to write a class to do these.
 */
public class ListOps {

    public static ArrayList intersect(ArrayList a, ArrayList b) {
	Hashtable tmp = new Hashtable();
	for (int i = 0; i < a.size(); i++) {
	    tmp.put(a.get(i), new Integer(1));
	}

	for (int i = 0; i < b.size(); i++) {
	    String key = (String) b.get(i);
	    Integer old = (Integer) tmp.get(key);
	    if (old != null) tmp.put(key, new Integer(old.intValue() + 1));
	    else tmp.put(key, new Integer(1));
	}
	
	ArrayList smaller, larger;
	if (a.size() > b.size()) {
	    smaller = b; 
	    larger = a;
	} else {
	    smaller = a;
	    larger = b;
	}

	ArrayList ret = new ArrayList();
	for (int i = 0; i < smaller.size(); i++) {
	    String key = (String) smaller.get(i);
	    Integer val = (Integer) tmp.get(key);
	    if (val.intValue() > 1) ret.add(key);
	}
	return ret;
    }
}