Bitmask based solution to N queens

n_queens_bitwise.rb

  def unsafe?(file, rank)
    get?(@ranks, rank) ||
      get?(@northwests, northwest(file, rank)) ||
      get?(@northeasts, northeast(file, rank))
  end

  def move!(file, rank)
    super(file, rank)
    @ranks = set!(@ranks, rank)
    @northwests = set!(@northwests, northwest(file, rank))
    @northeasts = set!(@northeasts, northeast(file, rank))
  end

  def unmove!(file, rank)
    super(file, rank)
    @ranks = clear!(@ranks, rank)
    @northwests = clear!(@northwests, northwest(file, rank))
    @northeasts = clear!(@northeasts, northeast(file, rank))
  end