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Documents authored by Fredslund-Hansen, Viktor

Document
DOI: 10.4230/LIPIcs.ISAAC.2021.23
Near-Optimal Distance Oracles for Vertex-Labeled Planar Graphs

Authors: Jacob Evald, Viktor Fredslund-Hansen, and Christian Wulff-Nilsen

Published in: LIPIcs, Volume 212, 32nd International Symposium on Algorithms and Computation (ISAAC 2021)

Abstract
Given an undirected n-vertex planar graph G = (V,E,ω) with non-negative edge weight function ω:E → ℝ and given an assigned label to each vertex, a vertex-labeled distance oracle is a data structure which for any query consisting of a vertex u and a label λ reports the shortest path distance from u to the nearest vertex with label λ. We show that if there is a distance oracle for undirected n-vertex planar graphs with non-negative edge weights using s(n) space and with query time q(n), then there is a vertex-labeled distance oracle with Õ(s(n)) space and Õ(q(n)) query time. Using the state-of-the-art distance oracle of Long and Pettie [Long and Pettie, 2021], our construction produces a vertex-labeled distance oracle using n^{1+o(1)} space and query time Õ(1) at one extreme, Õ(n) space and n^o(1) query time at the other extreme, as well as such oracles for the full tradeoff between space and query time obtained in their paper. This is the first non-trivial exact vertex-labeled distance oracle for planar graphs and, to our knowledge, for any interesting graph class other than trees.
Cite as

Jacob Evald, Viktor Fredslund-Hansen, and Christian Wulff-Nilsen. Near-Optimal Distance Oracles for Vertex-Labeled Planar Graphs. In 32nd International Symposium on Algorithms and Computation (ISAAC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 212, pp. 23:1-23:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{evald_et_al:LIPIcs.ISAAC.2021.23,
  author =	{Evald, Jacob and Fredslund-Hansen, Viktor and Wulff-Nilsen, Christian},
  title =	{{Near-Optimal Distance Oracles for Vertex-Labeled Planar Graphs}},
  booktitle =	{32nd International Symposium on Algorithms and Computation (ISAAC 2021)},
  pages =	{23:1--23:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-214-3},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{212},
  editor =	{Ahn, Hee-Kap and Sadakane, Kunihiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2021.23},
  URN =		{urn:nbn:de:0030-drops-154566},
  doi =		{10.4230/LIPIcs.ISAAC.2021.23},
  annote =	{Keywords: distance oracle, vertex labels, color distance oracle, planar graph}
}
Document
DOI: 10.4230/LIPIcs.ISAAC.2021.25
Truly Subquadratic Exact Distance Oracles with Constant Query Time for Planar Graphs

Authors: Viktor Fredslund-Hansen, Shay Mozes, and Christian Wulff-Nilsen

Published in: LIPIcs, Volume 212, 32nd International Symposium on Algorithms and Computation (ISAAC 2021)

Abstract
We present a truly subquadratic size distance oracle for reporting, in constant time, the exact shortest-path distance between any pair of vertices of an undirected, unweighted planar graph G. For any ε > 0, our distance oracle requires O(n^{5/3+ε}) space and is capable of answering shortest-path distance queries exactly for any pair of vertices of G in worst-case time O(log (1/ε)). Previously no truly sub-quadratic size distance oracles with constant query time for answering exact shortest paths distance queries existed.
Cite as

Viktor Fredslund-Hansen, Shay Mozes, and Christian Wulff-Nilsen. Truly Subquadratic Exact Distance Oracles with Constant Query Time for Planar Graphs. In 32nd International Symposium on Algorithms and Computation (ISAAC 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 212, pp. 25:1-25:12, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{fredslundhansen_et_al:LIPIcs.ISAAC.2021.25,
  author =	{Fredslund-Hansen, Viktor and Mozes, Shay and Wulff-Nilsen, Christian},
  title =	{{Truly Subquadratic Exact Distance Oracles with Constant Query Time for Planar Graphs}},
  booktitle =	{32nd International Symposium on Algorithms and Computation (ISAAC 2021)},
  pages =	{25:1--25:12},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-214-3},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{212},
  editor =	{Ahn, Hee-Kap and Sadakane, Kunihiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2021.25},
  URN =		{urn:nbn:de:0030-drops-154586},
  doi =		{10.4230/LIPIcs.ISAAC.2021.25},
  annote =	{Keywords: distance oracle, planar graph, shortest paths, subquadratic}
}
Document
Track A: Algorithms, Complexity and Games
DOI: 10.4230/LIPIcs.ICALP.2021.64
Decremental APSP in Unweighted Digraphs Versus an Adaptive Adversary

Authors: Jacob Evald, Viktor Fredslund-Hansen, Maximilian Probst Gutenberg, and Christian Wulff-Nilsen

Published in: LIPIcs, Volume 198, 48th International Colloquium on Automata, Languages, and Programming (ICALP 2021)

Abstract
Given an unweighted digraph G = (V,E), undergoing a sequence of edge deletions, with m = |E|, n = |V|, we consider the problem of maintaining all-pairs shortest paths (APSP). Whilst this problem has been studied in a long line of research [ACM'81, FOCS'99, FOCS'01, STOC'02, STOC'03, SWAT'04, STOC'13] and the problem of (1+ε)-approximate, weighted APSP was solved to near-optimal update time Õ(mn) by Bernstein [STOC'13], the problem has mainly been studied in the context of an oblivious adversary which fixes the update sequence before the algorithm is started. In this paper, we make significant progress on the problem for an adaptive adversary which can perform updates based on answers to previous queries: - We first present a deterministic data structure that maintains the exact distances with total update time Õ(n³). - We also present a deterministic data structure that maintains (1+ε)-approximate distance estimates with total update time Õ(√m n²/ε) which for sparse graphs is Õ(n^{2+1/2}/ε). - Finally, we present a randomized (1+ε)-approximate data structure which works against an adaptive adversary; its total update time is Õ(m^{2/3}n^{5/3} + n^{8/3}/(m^{1/3}ε²)) which for sparse graphs is Õ(n^{2+1/3}/ε²). Our exact data structure matches the total update time of the best randomized data structure by Baswana et al. [STOC'02] and maintains the distance matrix in near-optimal time. Our approximate data structures improve upon the best data structures against an adaptive adversary which have Õ(mn²) total update time [JACM'81, STOC'03].
Cite as

Jacob Evald, Viktor Fredslund-Hansen, Maximilian Probst Gutenberg, and Christian Wulff-Nilsen. Decremental APSP in Unweighted Digraphs Versus an Adaptive Adversary. In 48th International Colloquium on Automata, Languages, and Programming (ICALP 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 198, pp. 64:1-64:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{evald_et_al:LIPIcs.ICALP.2021.64,
  author =	{Evald, Jacob and Fredslund-Hansen, Viktor and Gutenberg, Maximilian Probst and Wulff-Nilsen, Christian},
  title =	{{Decremental APSP in Unweighted Digraphs Versus an Adaptive Adversary}},
  booktitle =	{48th International Colloquium on Automata, Languages, and Programming (ICALP 2021)},
  pages =	{64:1--64:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-195-5},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{198},
  editor =	{Bansal, Nikhil and Merelli, Emanuela and Worrell, James},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2021.64},
  URN =		{urn:nbn:de:0030-drops-141337},
  doi =		{10.4230/LIPIcs.ICALP.2021.64},
  annote =	{Keywords: Dynamic Graph Algorithm, Data Structure, Shortest Paths}
}
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