n_queens

n_queens is a Ruby gem that solves the N-Queens problem using the repository's existing solver logic (backtracking and bitmask-based methods), wrapped in a clean public API.

The underlying algorithms in includes/ are preserved as-is.

Installation

Add this line to your application's Gemfile:

gem "n_queens"

Then install:

bundle install

Or install directly:

gem install n_queens

Usage

require "n_queens"

solver = NQueens::Solver.new(8)
result = solver.solve

result.n         # => 8
result.count     # => 92
result.solutions # => [[0,4,7,5,2,6,1,3], ...]
result.method    # => :backtracking
result.duration  # => elapsed seconds as Float

Method Dispatch

NQueens::Solver automatically selects the method by board size:

• n <= 10: backtracking (:backtracking)
• 11..17: parallel bitmask (:parallel_bitmask)
• n >= 18: parallel bitmask to file (:parallel_bitmask)

For n >= 18, result.solutions is nil and result.count is read from output files created by the existing solver path.

Known Counts

The gem includes OEIS A000170 ground-truth counts:

NQueens::KNOWN_COUNTS[1]  # => 1
NQueens::KNOWN_COUNTS[4]  # => 2
NQueens::KNOWN_COUNTS[8]  # => 92
NQueens::KNOWN_COUNTS[12] # => 14200
NQueens::KNOWN_COUNTS[14] # => 365596

Values are included for n = 1..15.

Version

NQueens::VERSION # => "1.0.0"

Development

Run specs:

bundle exec rspec

Build gem:

gem build n_queens.gemspec

License

MIT. See LICENSE.md.