def testGetNeighbourOfOutOfRangeTooLowCell(self):
maze = Maze(4, 4)
with self.assertRaises(
expected_exception=IndexError,
msg="`cellIndex` out of range (-5 not between 0 and 15).",
):
_ = maze.getNeighboursOfCell(-5)
class RecursiveBacktracker(MazeGenerator):
"""Recursive Backtracker maze generation algorithm implementation.
| Here’s the mile-high view of recursive backtracking:
|
| • Choose a starting point in the field.
| • Randomly choose a wall at that point and carve a passage through to the adjacent cell, but only if the adjacent cell has not been visited yet.
| This becomes the new current cell.
| • If all adjacent cells have been visited, back up to the last cell that has uncarved walls and repeat.
| • The algorithm ends when the process has backed all the way up to the starting point.
> Source - http://weblog.jamisbuck.org/2010/12/27/maze-generation-recursive-backtracking
"""
__maze: MazeProtocol
__visitedOrNotCells: List[
bool] # the cell index is the position in the list
__size: XY
# the stack of positions
__positionsStack: Stack[int]
def __init__(self, size: XY) -> None:
# check size is valid
self._testSizeIsValidWithException(size)
self.__size = size
# initialize a Maze full of walls
self.__maze = Maze(self.__size.x, self.__size.y, walls=True)
# get the last cell index of the maze, so we can initialise __visitedOrNotCells to a list of False (nothing visited yet)
lastIndex = self.__maze.getIndexFromCoordinates(
XY(self.__size.x - 1, self.__size.y - 1))
# init __visitedOrNotCells to a list of False with the length of the max index of cells
self.__visitedOrNotCells = [False] * (lastIndex + 1)
def generate(self) -> MazeProtocol:
# start our maze generator in the top left of the maze
start = XY(0, 0)
# init positionsStack to a new empty stack of type int
self.__positionsStack = Stack[int]()
# Convert the `start` position to the same cell's index in the maze, and push to the positions stack
self.__positionsStack.push(
# get the index of the `start` posotion
self.__maze.getIndexFromCoordinates(start))
# set the starting cell as visited
self.__visitedOrNotCells[self.__positionsStack.peek()] = True
# while the positions stack is not empty, so we automatically exit the loop when visited all cells and back at start
while not self.__positionsStack.isEmpty():
randomCellChoice: Optional[int] = None
# this loop tries to find a random cell to visit out of the unvisited neighbours of the current cell
while randomCellChoice is None:
# if we've ran out of positions to backtrack to, and therefore made the entire maze
if self.__positionsStack.isEmpty():
break
# get a list of unvisited adjacent cells
neighbourCells = self.__maze.getNeighboursOfCell(
# get the current position by peeking the stack.
# don't pop because we want the item to remain on the stack,
# so we can backtrach through it.
self.__positionsStack.peek())
# Filter the neighbourCells by whether they've been visited or not
# create a lambda to return whether or not a cell at index has been visited, but return the inverse because we are _filtering_ the cells!
checkIsVisited: Callable[
[int],
bool] = lambda cellIndex: not self.__visitedOrNotCells[
cellIndex]
# …and filter the neighbourCells by this lambda, and put it into the list `unvisitedWalls`
unvisitedWalls = list(filter(checkIsVisited, neighbourCells))
# check that there are unvisited walls
if len(unvisitedWalls) > 0:
# choose a random wall
randomCellChoice = randomChoice(unvisitedWalls)
# set the next cell to visited
self.__visitedOrNotCells[randomCellChoice] = True
else:
# all the cells here have been visited
# so back up to the last cell, by popping the positionsStack
self.__positionsStack.pop()
# if the cell hasn't been chosen, and therefore we've explored the whole maze
if randomCellChoice is None:
# break so we can return the completed maze
break
# carve a passage through to the adjacent cell
self.__maze.removeWallBetween(
cellAIndex=self.__positionsStack.peek(),
cellBIndex=randomCellChoice,
)
# push the choice to the positionsStack so it is our next one
self.__positionsStack.push(randomCellChoice)
return self.__maze