A C++ implementation of a fast and space-efficient algorithm converting the LZ77 parsing into a straight-line grammar. The algorithm is based on AVL grammars introduced by Rytter [TCS, 2003]. Our main improvements are: delayed ("lazy") merging of nonterminals, and utilizing Karp-Rabin fingerprints.

For more detailed description of the algorithm and reports of experimental evaluation, refer to the following paper.

@inproceedings{lazyavl,
  author =      {Dominik Kempa and Ben Langmead},
  title =       {Fast and Space-Efficient Construction of {AVL}
                 Grammars from the {LZ77} Parsing},
  booktitle =   {29th Annual European Symposium on Algorithms
                 (ESA 2021)},
  pages =       {56:1--56:14},
  year =        {2021},
  doi =         {10.4230/LIPIcs.ESA.2021.56},
}

The above paper is available on arXiv at https://arxiv.org/abs/2105.11052.

The latest version of this code is available from https://github.com/dominikkempa/lz77-to-slp.

Lazy-AVLG is compiled by simply typing make in the directory containing this README. This will build the executable called lz_to_grammar. The simplest usage of Lazy-AVLG is as follows. Suppose the input LZ77 parsing (which can be computed using the program in tools/text_to_lz) is located in /data/input.txt.lz77. Then, to compute the lazy AVL grammar of input.txt, type:

$ ./lz_to_grammar /data/input.txt.lz77

This will write the output grammar to /data/input.txt.lz77.slg. For details of the encoding of the grammar, see the function write_to_file in include/lazy_avl_grammar/lazy_avl_grammar.hpp.

If you use this code, please cite the paper mentioned above. Lazy-AVLG is released under the MIT/X11 license. See the file LICENCE for more details.