spiral_code_golf.rb

num = ARGV[0].to_i
x = num
y = num - 2

grid = Array.new(y) { Array.new(x, '*')}

required_spiral_depth = x / 4 + 1

(1..required_spiral_depth*2).step(2) do |spiral_depth|
  (spiral_depth..y-spiral_depth).each do |i|
    grid[i][x-1-spiral_depth] = ' '
  end

  (spiral_depth..x-1-spiral_depth).each do |i|
    grid[spiral_depth][i] = ' '
  end

  (spiral_depth..y-1-spiral_depth).each do |i|
    grid[i][spiral_depth] = ' '
  end

  (spiral_depth..x-1-spiral_depth-2).each do |i|
    grid[y-1-spiral_depth][i] = ' '
  end
end

grid.each do |row|
  print row
  puts
end