class Queen
  def initialize( column, neighbor )
    @row      = 1
    @col      = column
    @neighbor = neighbor
  end

  def find_solution
    while ( @neighbor && @neighbor.can_attack(@row, @col) )
      unless self.advance
        return false
      end
    end
    return true    
  end

  def advance
    if ( @row < 8 )
      @row += 1
      return self.find_solution
    end

    if @neighbor
      unless @neighbor.advance
        return false
      end
      unless @neighbor.find_solution
        return false
      end
    else
      return false
    end

    @row = 1
    return self.find_solution
  end

  def can_attack( row, col )
    col_diff = col - @col
    row_candidates = [ @row, @row + col_diff, @row - col_diff ]
    if row_candidates.include?( row )
      return true
    end
    if @neighbor
      return @neighbor.can_attack( row, col )
    end
    return false
  end

  def to_s
    str = ""
    if @neighbor
      str = @neighbor.to_s
    end
    str + "column #@col #@row\n"
  end
end

def go
  last_queen = nil
  (1..8).each do |column|
    last_queen = Queen.new( column, last_queen )
    last_queen.find_solution
    # puts last_queen
  end
  puts last_queen
end

go