public class CheckedList
{
   //the Checked List vector
   public AVLDictionary  Checked_list;
   
   CheckedList() {
	   Checked_list = new AVLDictionary(new StringComparator( ));  
   }
//
//
   String Formkey(Board b) {
	   String key = "";	   
	   for(int i=0; i<4; i++)
		   for(int j=0; j<4; j++) 
			   key += Integer.toHexString(b.PuzzBoard[i][j]);
	   return key;
   }
   //
   //
   boolean isExternal(Position p) {
	   return Checked_list.isExternal(p);
   }
   //
   //
   boolean ExistsInList (Board SuccBoard) {	   
	return !isExternal( Checked_list.find( Formkey(SuccBoard) ) );
   }
//
//
   void AddToList (Board SuccBoard) {
       Checked_list.insert(Formkey(SuccBoard), SuccBoard);
   }
  
}