https://twitter.com/Code_60/status/589754550900260864

maze.rb

def print_maze(width, height, hori_walls, vert_walls)
  puts ' ' + '-' * (width * 2 - 1)
  (height - 1).times do |y|
    print '|'
    (width - 1).times do |x|
      print ' '
      print hori_walls[y][x] ? '|' : ' '
    end
    puts ' |'

    width.times do |x|
      print ' '
      print vert_walls[y][x] ? '-' : ' '
    end
    puts
  end
  print '|'
  (width - 1).times do |x|
    print ' '
    print hori_walls[height - 1][x] ? '|' : ' '
  end
  puts ' |'
  puts ' ' + '-' * (width * 2 - 1)
end

def generate_maze(width, height)
  # Walls between horizontally adjacent cells
  hori_walls = []
  height.times { hori_walls << Array.new(width - 1).map { true } }
  # Walls between vertically adjacent cells
  vert_walls = []
  (height - 1).times { vert_walls << Array.new(width).map { true } }

  visited = []
  (width * height).times { visited << false }

  x, y = [0, 0]
  stack = []
  while visited.include?(false)
    neighbors = []
    neighbors << [x - 1, y] if x > 0 && !visited[y * width + x - 1]
    neighbors << [x + 1, y] if x < width - 1 && !visited[y * width + x + 1]
    neighbors << [x, y - 1] if y > 0 && !visited[(y - 1) * width + x]
    neighbors << [x, y + 1] if y < height - 1  && !visited[(y + 1) * width + x]
    if neighbors.empty?
      if stack.empty?
        index = visited.map.with_index.select { |v, i| !v }.sample[1]
        x, y = index % width, index / width
        visited[y * width + x] = true
      else
        x, y = stack.pop
      end
    else
      neighbor = neighbors.sample
      stack << [x, y]
      if neighbor[0] == x
        vert_walls[[neighbor[1], y].min][x] = false
      else
        hori_walls[y][[neighbor[0], x].min] = false
      end
      x, y = neighbor
      visited[y * width + x] = true
    end
  end
  print_maze(width, height, hori_walls, vert_walls)
end

# generate_maze(10, 10)
#  -------------------
# |         |   |     |
#      -       -   -
# | | |   | |   |   | |
#    -   -   -     -
# |   | |     | | |   |
#  -     - -
# | | | |   |   | | | |
#            -       -
# |   |   |   | | |   |
#    -   - -   -   -
# | | | |   |     |   |
#        -   - - -
# | |   |   | |     | |
#    -           - -
# |   |   |   | |   | |
#  -   - -   -     -
# | |     | |   |     |
#    - -   -   -   - -
# |           |       |
#  -------------------