I am trying to write a program that solves a maze recursively. When a step has been made, an 'x' character is placed at that position in the maze and the maze is printed, if the maze reaches a dead end it backtracks its last recursive step by removing the 'x' from that position.
When run, the program always stops at the first step; it does not solve the maze completely
I have tried:
-Hardcoding each consecutive step to take to avoid a wall in the maze (but this defeats the purpose of using recursion)
-Starting the first step to take randomly (but this results in ArrayIndexOutOfBoundsException)
import java.util.Random;
public class MazeTraversalWithRecursiveBacktracking
{
private static Random random = new Random();
public static void main(String args[])
{
char [][] maze = {{'#', '#', '#', '#', '#', '#','#', '#', '#', '#', '#', '#'},
{'#', '.', '.', '.', '#', '.','.', '.', '.', '.', '.', '#'},
{'.', '.', '#', '.', '#', '.','#', '#', '#', '#', '.', '#'},
{'#', '#', '#', '.', '#', '.','.', '.', '.', '#', '.', '#'},
{'#', '.', '.', '.', '.', '#','#', '#', '.', '#', '.', '.'},
{'#', '#', '#', '#', '.', '#','.', '#', '.', '#', '.', '#'},
{'#', '.', '.', '#', '.', '#','.', '#', '.', '#', '.', '#'},
{'#', '#', '.', '#', '.', '#','.', '#', '.', '#', '.', '#'},
{'#', '.', '.', '.', '.', '.','.', '.', '.', '#', '.', '#'},
{'#', '#', '#', '#', '#', '#','.', '#', '#', '#', '.', '#'},
{'#', '.', '.', '.', '.', '.','.', '#', '.', '.', '.', '#'},
{'#', '#', '#', '#', '#', '#','#', '#', '#', '#', '#', '#'}};
printMaze(maze);
mazeTraversal(maze, 2, 0);
}
public static void mazeTraversal(char [][] maze, int currX, int currY)
{
int choice = -1;
try
{
maze[currX][currY] = 'x';
printMaze(maze);
boolean chosen = false;
if ((currX == 4) && (currY == 11)) //end of the maze
{
System.out.println("Maze completed");
return;
}
while(!chosen)
{
choice = 1;
//System.out.println("Choice "+choice);
if (choice == 0)
{
if (maze[currX-1][currY] == '.')//up
{
System.out.println("Chose up");
chosen = true;
}
else
choice = random.nextInt(4);
}
else if (choice == 1)
{
if (maze[currX][currY+1] == '.')//right
{
System.out.println("Chose right");
chosen = true;
}
else
choice = random.nextInt(4);
}
else if (choice == 2)
{
if (maze[currX+1][currY] == '.')//down
{
System.out.println("Chose down");
chosen = true;
}
else
choice = random.nextInt(4);
}
else if (choice == 3)
{
if (maze[currX][currY-1] == '.')//left
{
System.out.println("Chose left");
chosen = true;
}
else
choice = random.nextInt(4);
}
else
{
System.out.println("Haven't chosen");
choice = random.nextInt(4);
}
//System.out.println(choice+" "+chosen);
}
System.out.println(choice+" "+chosen);
if (choice == 0)
mazeTraversal(maze,currX-1,currY);
else if (choice == 1)
mazeTraversal(maze,currX,currY+1);
else if (choice == 2)
mazeTraversal(maze,currX+1,currY);
else if (choice == 3)
mazeTraversal(maze,currX,currY-1);
else //backup
{
recursiveBacktrack(maze, currX, currY);
}
}
catch(ArrayIndexOutOfBoundsException ex)
{
ex.printStackTrace();
System.out.println("Maze finished with choice = "+choice);
}
}
public static void recursiveBacktrack(char [][]maze, int currX, int currY)
{
maze[currX][currY] = ' ';
}
public static void printMaze(char maze[][])
{
for(int i = 0; i < 12; ++i)
{
for(int j = 0; j < 12; ++j)
{
System.out.print(maze[i][j]+" ");
}
System.out.println();
}
System.out.println();
System.out.println();
}
}
Expected Result: The expected result is for the maze to be solved recursively showing each attempt by reprinting the entire maze after each recursive step. '#' is a wall, '.' is a free space and 'x' is a spaced that has been occupied.
Actual Result: The actual result I get, as said previously is just the first recursion step after which the program loops indefinitely.
Error Message: Occasionally, I get the error message ArrayIndexOutOfBoundsException: -1
Let's first see how isValidDirection
and isSolution
should work like:
public boolean isValidDirection(x, y) {
return ((x < maze.length) &&
(x >= 0) &&
(y < maze[x].length) &&
(y >= 0) &&
(maxe[x][y] == '.'));
}
public boolean isSolution(x, y) {
return isValidDirection(x, y) && (((x % maze.length) - 1 == 0) || ((y % maze[x].length) - 1 == 0));
}
Let's implement the maze runner:
public boolean mazeRunner(x, y) {
if (!isValidDirection) {
//TODO: output the attempt
}
maze[x][y] = 'x';
//add (x,y) to current attempt
//we need to count attempt length
if (isSolution(x, y)) {
//TODO: output the successful attempt
} else if ((
(mazeRunner(x - 1, y)) ||
(mazeRunner(x + 1, y)) ||
(mazeRunner(x, y - 1)) ||
(mazeRunner(x, y + 1))
) == false) {
//TODO: Output the current failed attempt
}
maze[x][y] = '.';
//TODO: remove (x, y) from the current attempt
}
public void startMazeRunning(char[][] maze, x, y) {
this.maze = maze;
}
Of course, you will need to ensure that all the members that are needed are defined and properly initialized.