Question

My homework is to determine if a maze is solvable of not using Queue. If it is, print the path. I can get Queue to get to the end but it says it’s unsolvable. When actually it is. If I change the Final check if Statement to:

if (queue.isEmpty())
    {
        System.out.println("The maze is solvable!");
    }
else
    {
        System.out.println("The maze is unsolvable!");
    }

Then it says it is solvable, but then when I try another maze that isn’t solvable it says it is solvable. Not sure where I’m going wrong.

I have a separate Point class that defines the Points and right, left, above and below positions. I have to use Point (0,0) to mark the start and Point (row-1,col-1) to mark the goal.

Let me know if you need more code. It is searching a char 2D array.

maze1.txt – (First Line Defines the # of Rows and Columns) – Is Solvable

7 12
..+.+.++++++
.++...++...+
..++.....+.+
+.+..++.+..+
+...++....++
+.+++..++..+
++++++++++..

Says it’s unsolvable

    QueueMaze
The maze is unsolvable!
p p + p + p + + + + + + 
p + + p p p + + p p p + 
p p + + p p p p p + p + 
+ p + p p + + p + p p + 
+ p p p + + p p p p + + 
+ p + + + p p + + p p + 
+ + + + + + + + + + p . 

mMethod for solving the Maze

public void queueMaze() {

char[][] storedMaze = copy(); 

LinkedList<Point> queue = new LinkedList<Point>();
    int count = 0;
    Point start = new Point(0,0);
    Point cur, end, above, right, left, below;

    Boolean solved = false;

queue.add(start); 

while (!queue.isEmpty())
    {
    //Store the first element position 0 in cur
        cur = queue.removeFirst();
        //System.out.println(cur.toString());

        //compare cur's points to the isEnd points
        //(row-1, col-1) if it is the end, break out
        //of the While
        if (isEnd(cur) && isSafe(cur))
        {
            //System.out.println("cur's final : " + cur.toString());
            end = cur;
            break;
        }

        //mark cur as visited with a P
    markVisited(cur, P);

        //check the position above cur to see if it is
        //
    right = cur.getRight(); 
    if (inBounds(right) && isSafe(right))
        {
            queue.add(right);
        }

        below = cur.getBelow(); 
    if (inBounds(below) && isSafe(below))
        {
            queue.add(below);
        }

        left = cur.getLeft(); 
    if (inBounds(left) && isSafe(left))
        {
            queue.add(left);
        }

        above = cur.getAbove(); 
    if (inBounds(above) && isSafe(above))
        {
            queue.add(above);
        }

}//while
//System.out.println("The queue size is: " + queue.size());

    if (!queue.isEmpty())
    {
        System.out.println("The maze is solvable!");
    }
else
    {
        System.out.println("The maze is unsolvable!");
    }

print();

returnMaze(storedMaze);
}

Answer 1

the queue being empty does not determine whether or not the maze is solved. the queue simply keeps track of which spaces still need to be checked. it is perfectly fine to come to the end of the maze with lots of spaces left to check in your queue.

it looks like if your if (isEnd(cur) && isSafe(cur)) is triggered, then the maze is solveable.