,
Shaily Verma
,
Nadym Mallek
Creative Commons Attribution 4.0 International license
Given an undirected graph G and an integer k, the Secluded Π-Subgraph problem asks you to find a maximum size induced subgraph that satisfies a property Π and has at most k neighbors in the rest of the graph. This problem has been extensively studied; however, there is no prior study of the problem in directed graphs. This question has been mentioned by Jansen et al. [ISAAC'23].
In this paper, we initiate the study of Secluded Subgraph problems in directed graphs by incorporating different notions of neighborhoods: in-neighborhood, out-neighborhood, and their union. Formally, we call these problems {In, Out, Total}-Secluded Π-Subgraph, where given a directed graph G and an integer k, we want to find an induced subgraph satisfying Π of maximum size that has at most k in/out/total-neighbors in the rest of the graph, respectively. We investigate the parameterized complexity of these problems for different properties Π. In particular, we prove the following parameterized results:
- We design an FPT algorithm for the Total-Secluded Strongly Connected Subgraph problem when parameterized by k.
- We show that the Out-Secluded ℱ-Free Subgraph problem with parameter k is W[1]-hard, where ℱ is a family of directed graphs except any subgraph of a star graph whose edges are directed towards the center. This result also implies that In/Out-Secluded DAG is W[1]-hard, unlike the undirected variants of the two problems, which are FPT.
- We design an FPT-algorithm for In/Out/Total-Secluded α-Bounded Subgraph when parameterized by k, where α-bounded graphs are a superclass of tournaments.
- For undirected graphs, we improve the best-known FPT algorithm for Secluded Clique by providing a faster FPT algorithm that runs in time 1.6181^k n^𝒪(1).
@InProceedings{schmidt_et_al:LIPIcs.ISAAC.2025.53,
author = {Schmidt, Jonas and Verma, Shaily and Mallek, Nadym},
title = {{A Parameterized Study of Secluded Structures in Directed Graphs}},
booktitle = {36th International Symposium on Algorithms and Computation (ISAAC 2025)},
pages = {53:1--53:21},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-408-6},
ISSN = {1868-8969},
year = {2025},
volume = {359},
editor = {Chen, Ho-Lin and Hon, Wing-Kai and Tsai, Meng-Tsung},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2025.53},
URN = {urn:nbn:de:0030-drops-249616},
doi = {10.4230/LIPIcs.ISAAC.2025.53},
annote = {Keywords: Secluded Subgraph, Parametrized Complexity, Directed Graphs, Strong Connectivity}
}