,
Frank Kammer
,
Johannes Meintrup
Creative Commons Attribution 4.0 International license
We call a graph G separable if a balanced separator can be computed for G of size O(n^ε) with ε < 1. Many real-world graphs are separable such as graphs of bounded genus, graphs of constant treewidth, and graphs excluding a fixed minor. In particular, the well-known planar graphs are separable. We present a succinct encoding of separable graphs G such that, after the encoding is computed, any number of depth-first searches (DFS) can be performed from any given start vertex, each in o(n) time and o(n) bits in the word RAM model. After the execution of a DFS, the succinct encoding of G is augmented such that the DFS tree is encoded inside the encoding while maintaining succinctness. Afterward, the encoding provides common DFS-related queries in constant time. These queries include queries such as lowest-common ancestor of two given vertices in the DFS tree or queries that output the lowpoint of a given vertex in the DFS tree. Furthermore, for planar graphs, we show that the succinct encoding can be computed in O(n) bits and expected linear time, and a compact variant can be constructed in O(n) time and bits. For other separable graph classes 𝒢 the runtime and space usage depends on the specific algorithms used to find balanced separators in graphs of 𝒢.
@InProceedings{elberfeld_et_al:LIPIcs.ISAAC.2025.29,
author = {Elberfeld, Michael and Kammer, Frank and Meintrup, Johannes},
title = {{Space-Efficient Depth-First Search via Augmented Succinct Graph Encodings}},
booktitle = {36th International Symposium on Algorithms and Computation (ISAAC 2025)},
pages = {29:1--29:16},
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.2025.29},
URN = {urn:nbn:de:0030-drops-249379},
doi = {10.4230/LIPIcs.ISAAC.2025.29},
annote = {Keywords: Depth-First Search, Succinct, Space Efficient, Separable Graphs, Planar Graphs, Table Lookup, r-Division}
}