public class IntSet {
   //OVERVIEW: IntSets are unbounded, mutable sets of integers.
   private Vector els;
   // the rep
  // constructors
   public IntSet(){
      //EFFECTS: Initializes this to be empty.
      els = new Vector( );
}
   // methods
   public void insert (int x) {
      //MODIFIES: this
      //EFFECTS: Adds x to the elements of this.
      Integer y = new Integer(x);
      if (getIndex(y) < 0) els.add(y);
    }

   public void remove (int x) {
      //MODIFIES: this
      //EFFECTS: Removes x from this.
      int i = getIndex(new Integer(x));
      if (i < 0) return;
      els.set(i, els.lastElement( ));
      els.remove(els.size( ) - 1);
   }

   public boolean isIn (int x) {
      //EFFECTS: Returns true if x is in this else returns false.
      return getIndex(new Integer(x)) >= 0;
   }

   private int getIndex (Integer x) {
      //EFFECTS: If x is in this returns index where x appears else returns -1.
      for (inti=0;i< els.size( ); i++)
         if (x.equals(els.get(i))) return i;
      return -1;
   }

   public int size( ){
      //EFFECTS: Returns the cardinality of this.
      return els.size( );
   }

   public int choose ( ) throws EmptyException {
      //EFFECTS: If this is empty throws EmptyException else
     //returns an arbitrary element of this.
          if (els.size( ) == 0) throw new EmptyException("IntSet.choose");
          return els.lastElement( );
  }
}