For an undirected graph π¦ = (π΅, π€), with n vertices and m edges, the densest subgraph problem, is to compute a subset S β π΅ which maximizes the ratio |π€_S|/|S|, where π€_S β π€ is the set of all edges of π¦ with endpoints in S. The densest subgraph problem is a well studied problem in computer science. Existing exact and approximation algorithms for computing the densest subgraph require Ξ©(m) time. We present near-linear time (in n) approximation algorithms for the densest subgraph problem on implicit geometric intersection graphs, where the vertices are explicitly given but not the edges. As a concrete example, we consider n disks in the plane with arbitrary radii and present two different approximation algorithms. As a by-product, we show a reduction from (shallow) range-reporting to approximate counting/sampling which seems to be new and is useful for other problems such as independent query sampling.
@InProceedings{harpeled_et_al:LIPIcs.STACS.2025.43, author = {Har-Peled, Sariel and Rahul, Saladi}, title = {{Approximating Densest Subgraph in Geometric Intersection Graphs}}, booktitle = {42nd International Symposium on Theoretical Aspects of Computer Science (STACS 2025)}, pages = {43:1--43:17}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-365-2}, ISSN = {1868-8969}, year = {2025}, volume = {327}, editor = {Beyersdorff, Olaf and Pilipczuk, Micha{\l} and Pimentel, Elaine and ThαΊ―ng, Nguy\~{Γͺ}n Kim}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2025.43}, URN = {urn:nbn:de:0030-drops-228697}, doi = {10.4230/LIPIcs.STACS.2025.43}, annote = {Keywords: Geometric intersection graphs, Densest subgraph, Range searching, Approximation algorithms} }
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