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We investigate the enumeration of dense subgraphs under two well-known relaxations of cliques: k-plexes and k-defective cliques. Our main contribution is a family of algorithms with improved worst-case and output-sensitive complexities, driven by a decomposition technique based on graph degeneracy. We first propose a worst-case output-size near-optimal algorithm to enumerate all maximal k-plexes of size at least 2k-1, achieving a total time complexity of 𝒪(n(dk)³ 2^d Δ^k), where d is the degeneracy and Δ the maximum degree of the input graph. We then refine this result to obtain a fixed-parameter tractable output-sensitive algorithm with complexity 𝒪(α f(k) p(dΔ)), where α is the number of solutions, f(k) is an arbitrary function of k, and p is a polynomial. We then extend this framework to the enumeration of k-defective cliques and also show a linear-time O(n) algorithm for the enumeration of 2-plexes for graphs with bounded degeneracy. To the best of our knowledge, these complexities are competitive with or better than the current state of the art.
@InProceedings{jiddou_et_al:LIPIcs.IPEC.2025.22,
author = {Jiddou, Mohamed and Manoussakis, George},
title = {{Efficient Enumeration of k-Plexes and k-Defective Cliques}},
booktitle = {20th International Symposium on Parameterized and Exact Computation (IPEC 2025)},
pages = {22:1--22:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-407-9},
ISSN = {1868-8969},
year = {2025},
volume = {358},
editor = {Agrawal, Akanksha and van Leeuwen, Erik Jan},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2025.22},
URN = {urn:nbn:de:0030-drops-251545},
doi = {10.4230/LIPIcs.IPEC.2025.22},
annote = {Keywords: Parameterized complexity, enumeration algorithms, maximal cliques enumeration}
}