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  ...Q
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  .Q..
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=head2 Example: Langford pairings

See L<https://en.wikipedia.org/wiki/Langford_pairing>.

  examples/langford$ perl -I. langford.pl -v 1 2 3 4 5
  Solutions for n = 1: 0
  Solutions for n = 2: 0
  Solutions for n = 3: 1
  3 1 2 1 3 2
  Solutions for n = 4: 1
  4 1 3 1 2 4 3 2
  Solutions for n = 5: 0

=head2 Example: N-pieces

Generalized version of N-queens: place N knights and Q queens on an AxB board. Quite slow, unfortunately.

  examples/npieces$ perl -I. npieces.pl 8 8 5 5
  Solution 1
  NN......
  ....Q...
  ......Q.
  NN......
  N.......
  .......Q
  .....Q..
  ..Q.....
  < snip >
  Solutions for 8x8, N=5, Q=5: 16

entire L<output|https://metacpan.org/dist/Algorithm-X-DLX/source/examples/npieces/npieces-solutions.txt>

=head2 Example: Polyominoes

The code can solve any polyomino puzzle, but for now the executable simply prints all solutions to Scott's pentomino problem:

  examples/polyomino$ perl -I. polyomino.pl | head -n8
  LLXCCVVV
  LXXXCVZZ
  LNXCCVZY
  LNT  ZZY
  NNT  WYY
  NTTTWWFY
  PPPWWFFF
  PPIIIIIF

entire L<output|https://metacpan.org/dist/Algorithm-X-DLX/source/examples/polyomino/solutions-to-scotts-pentomino.txt>

=head1 DISCLAIMER

Author of the originating C++ sources, of which this distribution is mostly a direct translation, 
is Johannes Laire at L<https://github.com/jlaire/dlx-cpp>.
Even all the examples, tests and most of the documentation are his.

=head1 COPYRIGHT AND LICENSE

The following copyright notice applies to all the files provided in
this distribution, unless explicitly noted otherwise.

This software is copyright (c) 2025 by Steffen Heinrich

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

=head1 SEE ALSO

Donald E. Knuth, Stanford University 2000 L<Dancing Links|http://arxiv.org/pdf/cs/0011047v1> 

L<Introduction to Exact Cover Problem and Algorithm X|https://www.geeksforgeeks.org/introduction-to-exact-cover-problem-and-algorithm-x/>

Peter Pfeiffer BSc, Linz 2023 L<Uncovering Exact Cover Encodings|https://epub.jku.at/obvulihs/download/pdf/9260418>

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