Teacher's solution for Sudoku_solver

Sudoku_solver

=begin
#PSEUDOCODE FOR PHASE 2
solve!

#STEP 1...next step is either step 2 or 3
return false if board is valid
  valid? => checks for duplicates
if attempt causes some repetition of number

#STEP 2...
return board if solved?
	solved? => check for no empty spaces #solved means it is valid and no empty spaces

#STEP 3...
if not solved or valid, the space is 'without a doubt' empty
	first find first empty space
	put each of those numbers from 1..9 and try to solve it #this is big... this is where the previous methods are reused
	(1..9).each |value|
		put value in empty space
		create a new game
		solve it
=end

class Sudoku
	attr_reader :board
	def initialize(board)
		@board = board.split("")
		prepare_row_columns_boxes
		puts @rows.inspect
		puts @columns.inspect
		puts @boxes.inspect
		puts valid?
		
	end
 
	def solve!
 
		return false unless valid?
		return @board.join if solved?
 
		next_empty_index = @board.index("0")
 
		(1..9).each do |attempt|
			@board[next_empty_index] = attempt
			solution = Sudoku.new(@board.join).solve!
			return solution if solution
		end
 
		return false
		
	end
 
	def valid?
		no_dups?(@rows) && no_dups?(@columns) && no_dups?(@boxes)
	end
 
	def solved?
		@board.count("0") == 0
	end
 
	private
 
	def prepare_row_columns_boxes
		@rows = Array.new(9) {Array.new}
		@columns = Array.new(9) {Array.new}
		@boxes = Array.new(9) {Array.new}
 
		@board.each_with_index do |value, index|
			next if value == "0"
			@rows[row_for(index)].push value
			@columns[column_for(index)].push value
			@boxes[box_for(index)].push value
		end
	end
 
	def row_for(index)
		index / 9 #BUGBUG
	end
 
	def column_for(index)
		index % 9 #BUGBUG
	end
 
	def box_for(index)
		box_column_co = column_for(index) / 3
		row_column_co = row_for(index) / 3
		box_column_co + (row_column_co * 3)
		# (column_for(index) / 3) + ((row_for(index) / 3) * 3)
	end
 
 
	def no_dups?(set)
		set.each do |subset|
			return false if subset.uniq.length != subset.length
		end
		true
	end
end
 
 
game = Sudoku.new('003020600900305001001806400008102900700000008006708200002609500800203009005010300')
 
puts game.solve!