sudoku_solver.rb

class Sudoku
  attr_reader :position, :current_cell_value

  def initialize(board_string)
    @board = []
    @board_string = board_string
    @position = [7,6] #[row, col]
    @board_string.split(//).each_slice(9) {|slice| @board << slice}
    @current_cell_value = @board[@position[0]][@position[1]]
      @box_coord_hash = { box1: [[0,0],[0,1],[0,2],[1,0],[1,1],[1,2],[2,0],[2,1],[2,2]], 
     box2: [[0,3],[0,4],[0,5],[1,3],[1,4],[1,5],[2,3], [2,4], [2,5]],
     box3: [[0,6],[0,7],[0,8],[1,6],[1,7],[1,8],[2,6],[2,7],[2,8]],
     box4: [[3,0],[3,1],[3,2],[4,0],[4,1],[4,2],[5,0],[5,1],[5,2]],
     box5: [[3,3],[3,4],[3,5],[4,3],[4,4],[4,5],[5,3],[5,4],[5,5]],
     box6: [[3,6],[3,7],[3,8],[4,6],[4,7],[4,8],[5,6],[5,7],[5,8]],
     box7: [[6,0],[6,1],[6,2],[7,0],[7,1],[7,2],[8,0],[8,1],[8,2]],
     box8: [[6,3],[6,4],[6,5],[7,3],[7,4],[7,5],[8,3],[8,4],[8,5]],
     box9: [[6,6],[6,7],[6,8],[7,6],[7,7],[7,8],[8,6],[8,7],[8,8]]
   }
  end

  def solve!
    until the_whole_board_has_been_solved?
      possibility_holder = []
      unless occupied?
        (1..9).each do |num|
          @current_cell_value = num.to_s
          unless already_in_the_row? || already_in_the_col? || already_in_the_box?
                possibility_holder << @current_cell_value
          end #check
        end
      end #occupied?


      if possibility_holder.length == 1
         @board[@position[0]][@position[1]] = possibility_holder.pop
      end
      update_position!
    end
  end

  def the_whole_board_has_been_solved?
    @board.each {|row| return false if row.include?("0")}
    true
  end

  def board
    @board
  end

  def call_row
    row_arry = []
    @board[@position[0]].each_with_index do |value, index|
      row_arry << value unless index == @position[1]
    end
    row_arry
  end

  def call_column
    col_arry = []
    @board.each_with_index do |row, index| 
      col_arry << row[@position[1]] unless index == @position[0]
    end
    col_arry
  end


  def find_box
    @box_coord_hash.each do |box_num, coord|
      return box_num if coord.include?(@position) 
    end
  end

  def already_in_the_row?
    call_row.each do |value|
      if @current_cell_value == value 
        return true
      end
    end
    false
  end

  def already_in_the_col?
    call_column.each do |value|
      if @current_cell_value == value
        return true
      end
    end
    false
  end

  def already_in_the_box?
    box_num = find_box
    box_grid_indices = @box_coord_hash[box_num].clone
    box_without_current_cell = box_grid_indices.delete_if do |x|
      x == @position
    end

    box_without_current_cell.each do |cell_coord|
      if @current_cell_value == @board[cell_coord[0]][cell_coord[1]]
        return true
      end
    end
    false
  end

  def occupied?
    @board[@position[0]][@position[1]] == "0" ? false : true
  end

  def update_position!
    if @position[1] < 8 
      @position[1] += 1
    elsif @position[1] == 8 
      if @position[0] == 8
        @position = [0,0]
      else
        @position[1] = 0
        @position[0] += 1
      end
    end

    @current_cell_value = @board[@position[0]][@position[1]]
  end

end

board_string = File.readlines('sample.unsolved.txt').first.chomp

game = Sudoku.new(board_string)

# # Remember: this will just fill out what it can and not "guess"


p game.solve!

p game.board