This gem is a ruby implementation of D.Knuth's paper "Dancing Link" : https://arxiv.org/abs/cs/0011047 It implements a solver for the "exact cover of a matrix" problem. For a given matrix of 0s and 1s, it finds a set of rows that contains exactly one "1" in each column. This can be used to implement a tetramino or a sudoku solver.
Add this line to your application's Gemfile:
gem 'exact_matrix_cover'
And then execute:
$ bundle
Or install it yourself as:
$ gem install exact_matrix_cover
Basic usage
require "exact_cover"
matrix =
[
[0, 0, 1, 0, 1, 1, 0],
[1, 0, 0, 1, 0, 0, 1],
[0, 1, 1, 0, 0, 1, 0],
[1, 0, 0, 1, 0, 0, 0],
[0, 1, 0, 0, 0, 0, 1],
[0, 0, 0, 1, 1, 0, 1]
]
solutions = ExactCover::CoverSolver.new(matrix).call
solutions.count
# => 1
solutions.first
# => [[1, 0, 0, 1, 0, 0, 0], [0, 1, 0, 0, 0, 0, 1], [0, 0, 1, 0, 1, 1, 0]]
# this corresponds to the 4th, 5th and first rows of the given matrix
You can iterate through all the solutions
require "exact_cover"
matrix =
[
[1, 1],
[0, 1],
[1, 0]
]
solutions = ExactCover::CoverSolver.new(matrix).call
solutions.count
# => 2
solutions.next
# => [[1, 1]]
solutions.next
# => [[1, 0], [0, 1]]
You can also pass a time limit to the cover solver. It will stop searching the solution space and raise a TimeLimitReached exception after the time limit has elapsed.
begin
solutions = ExactCover::CoverSolver.new(matrix, 10).call
rescue ExactCover::CoverSolver::TimeLimitReached
end
After checking out the repo, run bin/setup
to install dependencies. Then, run rake spec
to run the tests. You can also run bin/console
for an interactive prompt that will allow you to experiment.
To install this gem onto your local machine, run bundle exec rake install
. To release a new version, update the version number in version.rb
, and then run bundle exec rake release
, which will create a git tag for the version, push git commits and tags, and push the .gem
file to rubygems.org.
Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/exact_cover.
The gem is available as open source under the terms of the MIT License.