sudoku_threading.rb

require 'matrix'

class Sudoku
  attr_reader :board
  def initialize(string)
    @board = self.create_board(string)
  end

  def create_board(string)
    array = string.split('').map(&:to_i)
    board = Matrix[*Array.new(9) { array.shift(9)}]
  end

  def print_board
    board_array = @board.to_a
    9.times do |col|
      board_array[col].each do |x|
        print x.to_s.ljust(2)
      end
      puts
    end
  end

  def flat_board
    board_array = @board.to_a
    board_array.flatten
  end

  def check_row_col(row,col)
    possible_matches = (1..9).to_a
    possible_matches -= @board.row(row).to_a
    possible_matches -= @board.column(col).to_a
  end

  def check_block(row,col)
    hash = {}
    @board.each_with_index do |num, row, col|
      hash[[row/3,col/3]] ||= []
      hash[[row/3,col/3]].push num
    end
    return hash[[row/3,col/3]]
  end


  def solve!
    possible_matches = []
    @possible_threads = []
    while flat_board.include?(0)
      solve_for_base_case(possible_matches)
      check_for_lowest_match(possible_matches)
      @possible_threads.sort_by! { |thread| thread[:possible_matches].length }
      puts @possible_threads
    end

    print_board
  end

  def check_for_lowest_match(possible_matches)
    while flat_board.include?(0)
      old_flat_board = flat_board
      @board.each_with_index do |num, row, col|
        if num == 0
          possible_matches = check_row_col(row,col)
          possible_matches -= check_block(row,col)
          @possible_threads << {value: num, row: row,col: col,possible_matches: possible_matches}
          check_for_unique_matches(possible_matches, row, col)
        end
      end
      if old_flat_board == flat_board
        puts "start thread mode"
        break
      end
    end
  end

  def solve_for_base_case(possible_matches)
    while flat_board.include?(0)
      old_flat_board = flat_board
      @board.each_with_index do |num, row, col|
        if num == 0
          possible_matches = check_row_col(row,col)
          possible_matches -= check_block(row,col)
          check_for_unique_matches(possible_matches, row, col)
        end
      end
      if old_flat_board == flat_board
        puts "start thread mode"
        break
      end
    end
  end

  def check_for_unique_matches(possible_matches, row, col)
    if possible_matches.length == 1
      new_board = @board.to_a
      new_board[row][col] = possible_matches.first
      @board = Matrix.rows(new_board)
      @success = true
    end
  end
end
game = Sudoku.new('003020600900305001001806400008102900700000008006708200002609500800203009005010300')
game.solve!
game = Sudoku.new('096040001100060004504810390007950043030080000405023018010630059059070830003590007')
game.solve!
# game = Sudoku.new('003020600900305001001806400008102900700000008006708200002609500800203009005010300')
# game.solve!
# game = Sudoku.new('003020600900305001001806400008102900700000008006708200002609500800203009005010300')
# game.solve!