,
Peng-Ting Lin
,
Meng-Tsung Tsai
Creative Commons Attribution 4.0 International license
Computing a topological ordering for an n-node directed acyclic graph (DAG) G is computationally challenging in streaming models. Chakrabarti et al. {[}SODA 2020{]} showed that in the insertion-only streaming model, every single-pass algorithm requires Ω(n²) space, and every k-pass algorithm requires n^{1+Ω(1/k)} space for any constant k ≥ 1.
We study the parameterized complexity of streaming algorithms for topological sorting, considering two parameters: the independence number α and the maximum displacement δ. Our results include an O(1/ε)-pass O(α n^{1+ε})-space streaming algorithm and an O(n^{1/2})-pass O(n+δ²)-space streaming algorithm. For dense random DAGs, both α and δ are small, allowing us to improve the state-of-the-art for topological sorting in random DAGs.
As applications, we show that strongly connected components (SCC) decomposition and 2-satisfiability (2-SAT) can be solved in O(1/ε) passes using O(α n^{1+ε}) space and O(α_I n^{1+ε}) space, respectively, where α_I denotes the independence number of the implication graph induced by the input 2-SAT instance.
@InProceedings{chen_et_al:LIPIcs.WADS.2025.18,
author = {Chen, Ho-Lin and Lin, Peng-Ting and Tsai, Meng-Tsung},
title = {{Parameterized Streaming Algorithms for Topological Sorting}},
booktitle = {19th International Symposium on Algorithms and Data Structures (WADS 2025)},
pages = {18:1--18:20},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-398-0},
ISSN = {1868-8969},
year = {2025},
volume = {349},
editor = {Morin, Pat and Oh, Eunjin},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.WADS.2025.18},
URN = {urn:nbn:de:0030-drops-242495},
doi = {10.4230/LIPIcs.WADS.2025.18},
annote = {Keywords: Independence Number, Chain Cover, SCC Decomposition, 2-Satisfiability}
}