We show that if p = O(1/n), then the Erdős-Rényi random graph G(n,p) with high probability admits a canonical labeling computable in time O(nlog n). Combined with the previous results on the canonization of random graphs, this implies that G(n,p) with high probability admits a polynomial-time canonical labeling whatever the edge probability function p. Our algorithm combines the standard color refinement routine with simple post-processing based on the classical linear-time tree canonization. Noteworthy, our analysis of how well color refinement performs in this setting allows us to complete the description of the automorphism group of the 2-core of G(n,p).
@InProceedings{verbitsky_et_al:LIPIcs.STACS.2025.75, author = {Verbitsky, Oleg and Zhukovskii, Maksim}, title = {{Canonical Labeling of Sparse Random Graphs}}, booktitle = {42nd International Symposium on Theoretical Aspects of Computer Science (STACS 2025)}, pages = {75:1--75:20}, 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 Thắng, Nguy\~{ê}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.2025.75}, URN = {urn:nbn:de:0030-drops-229003}, doi = {10.4230/LIPIcs.STACS.2025.75}, annote = {Keywords: Graph isomorphism, random graphs, canonical labeling, color refinement} }
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