sudoku_solver.rb

class SudokuSolver
  
  def initialize(puzzle)
    @@p = puzzle.split(//)   
  end
  
#Algorithm to solve the sudoku puzzle
  def solver
    
    #81 times for each block in the puzzle
    81.times do |j|
      next if @@p[j].to_i!=0
  
      candidatesArray = getCandidates(j)                   
      
      candidatesArray.each  do |v|      
           @@p[j]=v.to_s
           foundAll = solver
           if(foundAll == true)
             return true
           end
      end
      
      # finished trying all the candidates, backtrack      
      @@p[j]=0  
      return false                       
    end
    
    return true
  end
    
  def getCandidates(j)
  
      Array array = [1,2,3,4,5,6,7,8,9]
      
      row = j/9 *9
      col = j%9
      
      #find the cells with the same row
      9.times do |k|
        m = @@p[row+k].to_i
        if(m)
          array.delete(m)
        end
      end

      #find the cells in the same column
      9.times do |k|
        m = @@p[k*9 + col].to_i
        if(m)
          array.delete(m)
        end
      end

      #find the cells in the same sub cube
      start_row = j/27 * 3
      start_col = j%9/3 * 3
      3.times do |t|
        3.times do |l|
          m =  @@p[(start_row + t)*9 + start_col + l].to_i
          if(m)
            array.delete(m)
          end
        end
      end

      return array
    
  end
  
  def printResult
    puts "\n\nThe Solution is:\n"
    print "+-----------------------------+\n|"
    1.upto(81) do |x|
      print " #{@@p[x-1]} "
      if x%3==0 and x%9 !=0
        print "|"
      end
      if x%9==0 and x%81 !=0
        print"|\n|-----------------------------|\n|"
      end
      if x%81==0
        puts "|"
      end        
    end
    puts "+-----------------------------+"
      
  end
end


question = "000700390090500000300240800700900200000000000003007008004026007000005060026001000"
answer = SudokuSolver.new(question)
puts "\n\n\nSolving puzzle, wait one moment..."
answer.solver
answer.printResult