/* This class has a method that finds a shortest solution to a given instance
** of the Slider Puzzle Problem, returning that solution in the form of a 
** String (that describes a sequence of moves).
**
** Authors: R. McCloskey and < STUDENT's NAME >
** Collaborated with: ...
** Known defects: ...
*/

public class SliderPuzzleSolver {

   /* Returns a String encoding a shortest sequence of moves leading from
   ** the given starting configuration to the standard goal configuration,
   ** or null if there is no such sequence.
   ** pre: !start.equals( the standard goal configuration )
   */
   public static String solution(SliderPuzzleConfig start) {
      int numRows = start.numRows();
      int numCols = start.numColumns();
      SliderPuzzleConfig standardGoal = new SliderPuzzleConfig(numRows, numCols);
      return solution(start, standardGoal);
   } 

   /* Returns a String encoding a shortest sequence of moves leading from
   ** the given starting configuration to the given goal configuration,
   ** or null if there is no such sequence.
   ** pre: !start.equals(goal)
   */
   public static String solution(SliderPuzzleConfig start,
                                 SliderPuzzleConfig goal) {
      return null;   // STUB
   }

}