//**************************************************
    //this solution uses a stack to keep track of possible
    //states/positions to explore; it marks the maze to remember the
    //positions that it's already explored.
    public void solveStack() {
		//create teh search queue
	Stack<MazePos> stack = new Stack<MazePos>(); 

	//create initial state and put it in the queue
	MazePos ins = new MazePos(START_I, START_J); 
	stack.push(ins); 

	//save the maze
	char[][] mazecopy = this.clone();

	MazePos crts = null;
	while (!stack.isEmpty()) {
	    
	    //get current state
	    crts = stack.pop(); 
	    
	    if (isFinal(crts)) break;

	    //mark it 
	   mark(crts); 
	    
	    //generate all possible states and enqueue them
	    MazePos next; 
	    next = crts.north(); 
	    if (isInMaze(next) && isClear(next)) stack.push(next); 
	    next = crts.east(); 
	    if (isInMaze(next) && isClear(next)) stack.push(next); 
	    next = crts.south(); 
	    if (isInMaze(next) && isClear(next)) stack.push(next); 
	    next = crts.west(); 
	    if (isInMaze(next) && isClear(next)) stack.push(next); 
	}
	
	//if you are here, either queue is empty or crts is final 
	if (crts!= null && isFinal(crts)) {
	    System.out.println("Got the solution"); 
	    //print the maze
	    print();
	} else {
	    System.out.println("NO solution"); 
	}


	//restore the maze
	restore(mazecopy); 	//create teh search queue

    }