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An implementation of the "Hunt and Kill" algorithm for generating mazes.
# --------------------------------------------------------------------
# An implementation of the "Hunt and Kill" algorithm. This is fairly
# similar to the recursive backtracking algorithm, except that there
# is no recursion, and it doesn't backtrack. :) The algorithm can
# get a little slow towards the end, where the "hunt" phase has to
# search over nearly the entire field to find a candidate cell, but
# it's guaranteed to finish (unlike Aldous-Broder and Wilson's), and
# it's still pretty fast.
# --------------------------------------------------------------------
# --------------------------------------------------------------------
# 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
IN = 0x10
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, 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|
print "\e[43m" if cy == y # cursor is yellow
if cell == 0 && y+1 < grid.length && grid[y+1][x] == 0
print " "
else
print((cell & S != 0) ? " " : "_")
end
print "\e[0m" if cy == y
if cell == 0 && x+1 < row.length && row[x+1] == 0
print((y+1 < grid.length && (grid[y+1][x] == 0 || grid[y+1][x+1] == 0)) ? " " : "_")
elsif cell & E != 0
print(((cell | row[x+1]) & S != 0) ? " " : "_")
else
print "|"
end
end
puts
end
end
# --------------------------------------------------------------------
# 4. Hunt and Kill algorithm
# --------------------------------------------------------------------
def walk(grid, x, y)
[N, S, E, W].shuffle.each do |dir|
nx, ny = x + DX[dir], y + DY[dir]
if nx >= 0 && ny >= 0 && ny < grid.length && nx < grid[ny].length && grid[ny][nx] == 0
grid[y][x] |= dir
grid[ny][nx] |= OPPOSITE[dir]
return [nx, ny]
end
end
nil
end
def hunt(grid)
grid.each_with_index do |row, y|
display_maze(grid, y)
sleep 0.02
row.each_with_index do |cell, x|
next unless cell == 0
neighbors = []
neighbors << N if y > 0 && grid[y-1][x] != 0
neighbors << W if x > 0 && grid[y][x-1] != 0
neighbors << E if x+1 < grid[y].length && grid[y][x+1] != 0
neighbors << S if y+1 < grid.length && grid[y+1][x] != 0
direction = neighbors[rand(neighbors.length)] or next
nx, ny = x + DX[direction], y + DY[direction]
grid[y][x] |= direction
grid[ny][nx] |= OPPOSITE[direction]
return [x, y]
end
end
nil
end
print "\e[2J" # clear the screen
x, y = rand(width), rand(height)
loop do
display_maze(grid)
sleep 0.02
x, y = walk(grid, x, y)
x, y = hunt(grid) unless x
break unless x
end
display_maze(grid)
# --------------------------------------------------------------------
# 5. Show the parameters used to build this maze, for repeatability
# --------------------------------------------------------------------
puts "#{$0} #{width} #{height} #{seed}"
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