,
Michał Pilipczuk
,
Amadeus Reinald
,
Marek Sokołowski
,
Michał Włodarczyk
Creative Commons Attribution 4.0 International license
Fix a parameter k ∈ ℕ. We give dynamic data structures that for a fully dynamic undirected graph G, updated over time by edge insertions and edge deletions, can answer the following queries: - Long (u,v)-path: Given u,v ∈ V(G), is there a path from u to v of length at least k? - Long (u,v)-detour: Given u,v ∈ V(G), is there a path from u to v of length at least dist_G(u,v)+k? - Even/odd (u,v)-path: Given u,v ∈ V(G), is there a path from u to v of even/odd length? The amortized time of executing an update or answering a query is 2^𝒪(k³) log n + 𝒪(log² n log² log n) in the first two cases, and 𝒪(log² n log² log n) in the last, where n is the number of vertices of G. The first result is in sharp contrast with known conditional lower bounds for reporting paths of length at most k. Specifically, there is no data structure supporting queries about (u,v)-paths of length at most two in time n^o(1) unless the Triangle Conjecture fails. Our main technical contribution is a mechanism of "delayed edge insertion" that works locally on the level of biconnected components.
@InProceedings{dadush_et_al:LIPIcs.ESA.2026.35,
author = {Dadush, Daniel and Pilipczuk, Micha{\l} and Reinald, Amadeus and Soko{\l}owski, Marek and W{\l}odarczyk, Micha{\l}},
title = {{Dynamic Detours}},
booktitle = {34th Annual European Symposium on Algorithms (ESA 2026)},
pages = {35:1--35:19},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-445-1},
ISSN = {1868-8969},
year = {2026},
volume = {388},
editor = {Bille, Philip and Pettie, Seth and Storandt, Sabine},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2026.35},
URN = {urn:nbn:de:0030-drops-271712},
doi = {10.4230/LIPIcs.ESA.2026.35},
annote = {Keywords: Dynamic algorithms, Fixed-parameter tractability}
}