// The list-based set, no ordering
public class SetAA extends LBS implements Set {

   public SetAA() {  super(); }

   // positions the list at element x if it is there, else return null
   private ListOfObjects locate(Element x) {
      ls.reset();
      while (!ls.atEnd()) {
         Element curr = (Element) ls.getItem();
         if (curr.elEquals(x)) return ls;
         ls.next();
      }
      return null;
   }

   public Element find(Element x) {
      if (locate(x) == null) return null;
      else return (Element)ls.getItem();
   }

   public void insert(Element x) {
      if (locate(x) == null) ls.insert(x);
   }

   public void delete(Element x) {
      if (locate(x) != null) ls.delete();
   }

   public boolean hasElement(Element x) {
      return locate(x) != null;
   }

   public void union(Set other) {
      if (this != other) {
         Element[] elems = other.getContents();
         for (int i=0; i < elems.length; ++i) {
            insert(elems[i]);
         }
      }
   }
   public void intersection(Set other) {
      if (this != other) {
         Element[] elems = getContents();
         for (int i=0; i < elems.length; ++i) {
            if (!other.hasElement(elems[i])) delete(elems[i]);
         }
      }
   }
   public void difference(Set other) {
      if (this != other) {
         Element[] elems = other.getContents();
         for (int i=0; i < elems.length; ++i) {
            delete(elems[i]);
         }
      }
   }

}