Swift Recursive Back Tracking Algorithm Not Working - algorithm

Question

Hi I have written a class in swift that should create a maze through a recursive backtracking algorithm. I seem to have a problem around the assignment of walls to my maze. But I can not crack it.
It would be great if I could get some help here, thank you!
Please find a description of the code below
2D Array Class - Pretty self explanatory. Give it a number of columns and rows and a default value, from there it generate the 2d array. The subscript methods allow you to set and get values.
class Array2D<T> {
let columns: Int
let rows: Int
var array : Array<Array<T?>>
init(columns: Int, rows: Int, repeatedValue: T?) {
self.columns = columns
self.rows = rows
var tmp = Array<T?>(count: rows, repeatedValue: repeatedValue)
array = Array<Array<T?>>(count: columns, repeatedValue: tmp)
}
subscript(column: Int, row: Int) -> T? {
get {
return array[column][row]
}
set(newValue) {
array[column][row] = newValue
}
}
}
DIR enum A enum which allows us to abstract ourselves from bits by assigning them names.
enum DIR : UInt8 {
case N = 1
case S = 2
case E = 4
case W = 8
case O = 0
}
Direction Class This class holds all the information about the Directions. It may be slightly an overkill. It allows you to get directions (N,S,E,W) in relation to a current location. You can also get the opposite direction.
class Direction {
var bit : DIR
var dx : Int
var dy : Int
init(bit: DIR, dx: Int, dy: Int) {
self.bit = bit
self.dx = dx
self.dy = dy
}
class func NORTH() -> Direction {
return Direction(bit: DIR.N, dx: 0, dy: -1)
}
class func SOUTH() -> Direction {
return Direction(bit: DIR.S, dx: 0, dy: 1)
}
class func EAST() -> Direction {
return Direction(bit: DIR.E, dx: 1, dy: 0)
}
class func WEST() -> Direction {
return Direction(bit: DIR.W, dx: -1, dy: 0)
}
func opposite() -> Direction {
switch(bit){
case DIR.N:
return Direction.SOUTH()
case DIR.S:
return Direction.NORTH()
case DIR.E:
return Direction.WEST()
case DIR.W:
return Direction.EAST()
default:
println("An error occured while returning the opposite of the direction with bit: \(bit)")
return Direction(bit: DIR.O, dx: 0, dy: 0)
}
}
}
RecursiveBackTracking Class This is where the magic happens. This class auto generates a maze given a width(x) and a height(y). The generateMaze() function does most of the work with the other functions in support. Everything here seems to work but I am still not getting the appropriate result. Potentially the problem may also by in the display() function.
class RecursiveBacktracking {
var x : Int
var y : Int
var maze : Array2D<UInt8>
init(x: Int, y: Int) {
self.x = x
self.y = y
maze = Array2D<UInt8>(columns: x, rows: y, repeatedValue: 0)
generateMaze(0, cy: 0)
display()
}
func generateMaze(cx: Int, cy: Int) {
var directions : [Direction] = [Direction.NORTH(),Direction.SOUTH(),Direction.EAST(),Direction.WEST()]
directions = shuffle(directions)
for dir in directions {
var nx : Int = cx + dir.dx
var ny : Int = cx + dir.dy
if between(nx, upper: x) && between(ny, upper: y) && getMazeObject(nx, y: ny) == 0 {
maze[cx,cy] = bitwiseOr(getMazeObject(cx, y: cy), b: dir.bit.rawValue)
maze[nx,ny] = bitwiseOr(getMazeObject(nx, y: ny), b: dir.opposite().bit.rawValue)
generateMaze(nx, cy: ny)
}
}
}
func bitwiseOr(a: UInt8, b: UInt8) -> UInt8 {
return a | b
}
func getMazeObject(x: Int, y: Int) -> UInt8 {
if var object = maze[x,y] {
return object
}else{
println("No object could be found at location: (\(x),\(y)).")
return 0
}
}
func between(v: Int, upper: Int) -> Bool {
return (v>=0) && (v<upper)
}
func shuffle<C: MutableCollectionType where C.Index == Int>(var list: C) -> C {
let count : Int = Int(countElements(list))
for i in 0..<(count - 1) {
let j = Int(arc4random_uniform(UInt32(count - i))) + i
swap(&list[i], &list[j])
}
return list
}
func display() {
for i in 0..<y {
// Draw North Edge
for j in 0..<x {
var bit : UInt8 = getMazeObject(j, y: i)
bit = bit & 1
if bit == 0 {
print("+---")
}else{
print("+ ")
}
}
println("+")
// Draw West Edge
for j in 0..<x {
var bit : UInt8 = getMazeObject(j, y: i)
bit = bit & 8
if bit == 0 {
print("| ")
}else{
print(" ")
}
}
println("|")
}
// Draw the bottom line
for j in 0..<x {
print("+---")
}
println("+")
}
}
Additional Information: This algorithm is based off of http://rosettacode.org/wiki/Maze#Java

Answer 1

The error is here:
var nx : Int = cx + dir.dx
var ny : Int = cx + dir.dy
The second cx should be cy.
Remark: There is some room for improvement in your code. As an example, the
bitwise or | is already defined for UInt8, so there is no need to define that
as a function. If you have fixed your code to work correctly, you might consider
to post it at http://codereview.stackexchange.com to get a review.