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An implementation of the Aldous-Broder algorithm for generating mazes.
# --------------------------------------------------------------------
# An implementation of Aldous-Broder's algorithm for generating mazes.
# This is an easy one to implement, but it is also one of the
# "dumbest" (meaning least intelligent) algorithms. It is not even
# guaranteed to finish, if you get really unlucky with the RNG.
# Watching the animation of its progress can be an exercise in
# frustration as you find yourself urging the cursor to JUST GO
# OVER THERE! Try and it see for yourself. :)
# --------------------------------------------------------------------
# NOTE: the display routine used in this script requires a terminal
# that supports ANSI escape sequences. Windows users, sorry. :(
# --------------------------------------------------------------------
# --------------------------------------------------------------------
# 1. Allow the maze to be customized via command-line parameters
# --------------------------------------------------------------------
width = (ARGV[0] || 10).to_i
height = (ARGV[1] || width).to_i
seed = (ARGV[2] || rand(0xFFFF_FFFF)).to_i
srand(seed)
grid = Array.new(height) { Array.new(width, 0) }
# --------------------------------------------------------------------
# 2. Set up constants to aid with describing the passage directions
# --------------------------------------------------------------------
N, S, E, W = 1, 2, 4, 8
DX = { E => 1, W => -1, N => 0, S => 0 }
DY = { E => 0, W => 0, N => -1, S => 1 }
OPPOSITE = { E => W, W => E, N => S, S => N }
# --------------------------------------------------------------------
# 3. A simple routine to emit the maze as ASCII
# --------------------------------------------------------------------
def display_maze(grid, cx=nil, cy=nil)
print "\e[H" # move to upper-left
puts " " + "_" * (grid[0].length * 2 - 1)
grid.each_with_index do |row, y|
print "|"
row.each_with_index do |cell, x|
if cx == x && cy == y
print "\e[43m" # cursor is yellow
elsif cell == 0
print "\e[47m" # unvisited is white
end
print((cell & S != 0) ? " " : "_")
print "\e[0m"
if cell & E != 0
print(((cell | row[x+1]) & S != 0) ? " " : "_")
else
print "|"
end
end
puts
end
end
# --------------------------------------------------------------------
# 4. The Aldous-Broder algorithm
# --------------------------------------------------------------------
print "\e[2J" # clear screen
x, y = rand(width), rand(height)
remaining = width * height - 1
while remaining > 0
display_maze(grid, x, y)
sleep 0.02
[N,S,E,W].shuffle.each do |dir|
nx, ny = x + DX[dir], y + DY[dir]
if nx >= 0 && ny >= 0 && nx < width && ny < height
if grid[ny][nx] == 0
grid[y][x] |= dir
grid[ny][nx] |= OPPOSITE[dir]
remaining -= 1
end
x, y = nx, ny
break
end
end
end
display_maze(grid)
# --------------------------------------------------------------------
# 5. Show the parameters used to build this maze, for repeatability
# --------------------------------------------------------------------
puts "#{$0} #{width} #{height} #{seed}"

defunkt commented Dec 31, 2010

This is great.

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