From: Christian Roese <croese@...>
Date: 2007-05-21T10:40:27+09:00
Subject: [QUIZ] Solution: Magic Squares (#124)

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Here goes!

#!/usr/bin/ruby -w
#########################
# Author: Christian Roese
# Filename: magicsquare.rb
# Date: 20-05-07
#########################
# Ruby Quiz #124 - Magic Squares

# behold, a rhodes magic square class!
class MagicSquare
  def initialize(size)
    @size = size
    @square = Array.new(size)
    @square.each_index { |i| @square[i] = Array.new(size, 0) }  # create
multidimensional array of zeroes
    # let's get started building this thing
    create
  end

  # primary function in this class; takes care of all the legwork by filling
in the magic
  # square with successive numbers
  def create
    stop = @size ** 2
    row = 0
    col = (@size - 1) / 2     # handy trick to find middle of zero-based
array
    1.upto(stop) do |num|
      @square[row][col] = num
      temp_row, temp_col = row - 1, col - 1
      temp_row = @size - 1 if temp_row < 0    # handle going off the deep
end and adjust accordingly
      temp_col = @size - 1 if temp_col < 0    # ...and here, too
      if @square[temp_row][temp_col] != 0     # check if prospective spot is
already filled
        temp_row, temp_col = row + 1, col     # if so, move down one spot
from initial square
      end
      # get ready for next iteration
      row = temp_row
      col = temp_col
    end
  end

  # pretty-printing function that displays the magic square in a box
  # looks alright until numbers get above 1,000...
  def pp
    rowsep = "+" + "-" * (@size * 6 - 1) + "+"  # IMPROVE ME: more dynamic
string for larger squares - perhaps dependent on @size^2
    rowfmt = "|" + " %3d |" * @size +"\n"       # IMPROVE ME: more dynamic
string for larger squares - perhaps dependent on @size^2
    puts rowsep
    @square.each do |sub|
      printf(rowfmt, *sub)
      puts rowsep
    end
  end

  # helper function to check row sum
  def magic_number(row=0)
    @square[row].inject { |sum, n| sum + n }
  end
  private :create
end

# grab cmd-line arg and convert it to a number
# NOTE: if to_i fails here, it returns a 0 which is then caught by the
if-then clause - no exceptions needed!
input = ARGV.shift.to_i

# prevent bad input
# NOTE: ignoring size == 1 since it's a trivial square
E_BADARG = 1
if input <= 2 || input % 2 == 0
  puts "Bad argument - must be an odd integer > 2"
  exit E_BADARG
end

# make a new square, print it fancily(?), and spit out the magic number for
kicks
sq = MagicSquare.new(input)
sq.pp
puts "magic number = #{sq.magic_number}"

--
Christian Roese

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