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An implementation of Kruskal's algorithm for generating mazes.
# --------------------------------------------------------------------
# An implementation of Kruskal's algorithm for generating mazes.
# Fairly expensive, memory-wise, as it requires memory proportional
# to the size of the entire maze, and it's not the fastest of the
# algorithms (what with all the set and edge management is has to
# do). Also, the mazes it generates tend to have a lot of very short
# dead-ends, giving the maze a kind of "spiky" look.
# --------------------------------------------------------------------
# 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
delay = (ARGV[3] || 0.01).to_f
srand(seed)
# --------------------------------------------------------------------
# 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. Data structures and methods to assist the algorithm
# --------------------------------------------------------------------
def display_maze(grid)
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|
print "\e[47m" if cell == 0
print((cell & S != 0) ? " " : "_")
if cell & E != 0
print(((cell | row[x+1]) & S != 0) ? " " : "_")
else
print "|"
end
print "\e[m" if cell == 0
end
puts
end
end
class Tree
attr_accessor :parent
def initialize
@parent = nil
end
def root
@parent ? @parent.root : self
end
def connected?(tree)
root == tree.root
end
def connect(tree)
tree.root.parent = self
end
end
grid = Array.new(height) { Array.new(width, 0) }
sets = Array.new(height) { Array.new(width) { Tree.new } }
# build the list of edges
edges = []
height.times do |y|
width.times do |x|
edges << [x, y, N] if y > 0
edges << [x, y, W] if x > 0
end
end
edges = edges.sort_by{rand}
# --------------------------------------------------------------------
# 4. Kruskal's algorithm
# --------------------------------------------------------------------
print "\e[2J" # clear the screen
until edges.empty?
x, y, direction = edges.pop
nx, ny = x + DX[direction], y + DY[direction]
set1, set2 = sets[y][x], sets[ny][nx]
unless set1.connected?(set2)
display_maze(grid)
sleep(delay)
set1.connect(set2)
grid[y][x] |= direction
grid[ny][nx] |= OPPOSITE[direction]
end
end
display_maze(grid)
# --------------------------------------------------------------------
# 5. Show the parameters used to build this maze, for repeatability
# --------------------------------------------------------------------
puts "#{$0} #{width} #{height} #{seed}"
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