#!/usr/bin/ruby

#	ulam.rb - Generates an Ulam spiral
#	Copyright (C) 2007  Guillem Cantallops Ramis <guillem-at-cantallops-dot-net>
#
#	This program is free software; you can redistribute it and/or
#	modify it under the terms of the GNU General Public License
#	as published by the Free Software Foundation; either version 2
#	of the License, or (at your option) any later version.
#
#	This program is distributed in the hope that it will be useful,
#	but WITHOUT ANY WARRANTY; without even the implied warranty of
#	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#	GNU General Public License for more details.
#
#	You should have received a copy of the GNU General Public License
#	along with this program; if not, write to the Free Software
#	Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

require "mathn"

class BinaryPrimeSequence < Prime

	def initialize
		super
		@number = 0
		@prime = self.next
	end

	def digit
		@number += 1
		if @number == 1 then
			1
		elsif @number == @prime then 
			@prime = self.next
			1
		else
			0
		end
	end

end

class SpiralWalker

	def initialize(dim)
		@dim = dim
		@x = @y = (@dim >> 1) + 1
		@step = 1
	end

	def path
		while (@step <= @dim)
			@step.times { break if @x > @dim or @y > @dim; yield @x, @y; @x += 1 }
			@step.times { break if @x > @dim or @y > @dim; yield @x, @y; @y -= 1 }
			@step += 1
			@step.times { break if @x > @dim or @y > @dim; yield @x, @y; @x -= 1 }
			@step.times { break if @x > @dim or @y > @dim; yield @x, @y; @y += 1 }
			@step += 1
		end
	end

end

exit unless (dim = Integer(ARGV[0])) > 0
dim |= 1
bps = BinaryPrimeSequence.new
sw = SpiralWalker.new(dim)
mtx = Array.new(dim) { Array.new(dim) { 0 } }
sw.path { |x, y| mtx[x-1][y-1] = bps.digit }
mtx.each { |row| row.each { |num| print num }; print "\n" }