sudoku.rb

class Sudoku
  def initialize(matrix)
    @matrix = matrix.split("\n").map(&:chars)
  end

  def run
    show
    step while @matrix.flatten.include?(' ')
  end

  def step
    @matrix.each_with_index do |l, i|
      l.each_with_index do |c, j|
        next if c != ' '

        candidates = ('1'..'9').to_a
        candidates.reject! do |n|
          l.include?(n) \
            || @matrix.map { |l| l[j] }.include?(n) \
            || @matrix.slice(i - (i - ((i / 3) * 3)), 3).map { |l|
                 l.slice(j - (j - ((j / 3) * 3)), 3)
               }.flatten.include?(n)
        end

        if candidates.count == 1
          @matrix[i][j] = candidates.first
          print "\n"
          show([i, j])
        end
      end
    end
  end

  def show(changed = [])
    # print "\e[2J\e[1;1H"
    print "+---+---+---\e[1m+\e[0m---+---+---\e[1m+\e[0m---+---+---+\n"
    @matrix.each_with_index do |l, i|
      print "|"
      l.each_with_index do |c, j|
        if [i, j] == changed
          print " \e[33m#{c}\e[0m "
        else
          print " #{c} "
        end
        print "\e[1m" if j == 2 || j == 5
        print "|"
        print "\e[0m" if j == 2 || j == 5
      end
      print "\n"
      print "\e[1m" if i == 2 || i == 5
      if i == 2 || i == 5
        print "+---+---+---+---+---+---+---+---+---+"
      else
        print "+---+---+---\e[1m+\e[0m---+---+---\e[1m+\e[0m---+---+---+"
      end
      print "\e[0m" if i == 2 || i == 5
      print "\n"
    end
  end
end

# Sudoku.new(<<MATRIX).run
# 64  3   7
# 5 1 7 9  
#        1 
#   49 8 6 
#  8   3 2 
#    4     
# 4  157 3 
# 2 83   4 
# 75     96
# MATRIX

Sudoku.new(<<MATRIX).run
   3549 6
2 6819   
   762   
427 315  
915 7    
6    5  7
   4     
5   2673 
 6 5   19
MATRIX