A class to print arbitrary Sudoku-style gride, given a list of numbers.

grid.rb

# A class to print arbitrary Sudoku-style grids, given a list of numbers
# Author: Ashok Menon, 01/09/2015

class Array
  def surround(delim)
    "#{delim}#{join delim}#{delim}"
  end
end

class Grid
  # Accepts a list of 81 numbers.
  # The first 9 are treated as the first row, the 2nd 9 as the 2nd row etc.
  # A value of 0 signifies an empty position in the grid.
  def initialize(nums)
    unless nums.length == NUM_ELEMS
      raise ArgumentError, "#{NUM_ELEMS} numbers required, I was given #{nums.length}"
    end
    @grid = nums.each_slice(GRID_WIDTH).to_a
  end

  def to_s
   @grid.each_slice(BOX_HEIGHT).map do |row_of_boxes|
     row_of_boxes.map do |row|
       row.each_slice(BOX_WIDTH).map do |box_row|
         box_row.map do |digit|
           digit == 0 ? '.' : digit.to_s
         end.surround(" " * NUM_PAD)
       end.surround("|")
     end.surround("\n")
   end.surround(H_BORDER)
  end

  BOX_WIDTH   = 3
  BOX_HEIGHT  = 3

  BOX_HCOUNT  = 3
  BOX_VCOUNT  = 3

  GRID_WIDTH  = BOX_WIDTH * BOX_HCOUNT
  GRID_HEIGHT = BOX_HEIGHT * BOX_VCOUNT
  NUM_ELEMS   = GRID_WIDTH * GRID_HEIGHT

  private
  NUM_PAD       = 1
  BOX_H_BORDER  = "-" * (NUM_PAD + (1 + NUM_PAD) * BOX_WIDTH)
  H_BORDER      = ([BOX_H_BORDER] * BOX_HCOUNT).surround("+")
end

if ARGV.length != 1
  puts "Usage: $ ruby #{__FILE__} [#{Grid::NUM_ELEMS} numbers, no spaces]"
  exit
end

input = ARGV.first.split("").map(&:to_i)
puts Grid.new(input).to_s