import java.util.*;

public class BackTrack 
{
  	protected Application app;


	/**
     	 * Initializes this BackTrack object from an application.
     	 * 
     	 * @param app the application 
     	 */    
    	public BackTrack (Application app) 
    	{
        	this.app = app;
    	} // constructor


    	/**
     	 * Attempts to reach a goal through a given position.
     	 * 
     	 * @param pos the given position.
     	 * 
     	 * @return true if the attempt succeeds; otherwise, false.
         */        
    	public boolean tryToReachGoal (Position pos)
    	{
        	boolean success = false;

        	Iterator<Position> itr = app.iterator (pos);

        	while (!success && itr.hasNext())
        	{
  	          	pos = itr.next();
        	    	if (app.isOK (pos))
            		{
                		app.markAsPossible (pos);
                		if (app.isGoal (pos))
                    			success = true;
                		else
                		{
                    			success = tryToReachGoal (pos);
                    			if (!success)
                        			app.markAsDeadEnd (pos);
                		} // goal not reached yet
            		} // pos may be on a path to a goal
        	} // while
        	return success;
    } // method tryToReachGoal

} // class BackTrack