ARRIVAL: Next stop in CLS

Bernd Gärtner, Thomas Dueholm Hansen, Pavel Hubácek, Karel Král, Hagar Mosaad, Veronika Slívová

4 Citations (Scopus)
9 Downloads (Pure)

Abstract

We study the computational complexity of Arrival, a zero-player game on n-vertex switch graphs introduced by Dohrau, Gärtner, Kohler, Matoušek, and Welzl. They showed that the problem of deciding termination of this game is contained in NP ∩ coNP. Karthik C. S. recently introduced a search variant of Arrival and showed that it is in the complexity class PLS. In this work, we significantly improve the known upper bounds for both the decision and the search variants of Arrival. First, we resolve a question suggested by Dohrau et al. and show that the decision variant of Arrival is in UP ∩ coUP. Second, we prove that the search variant of Arrival is contained in CLS. Third, we give a randomized O(1.4143n)-time algorithm to solve both variants. Our main technical contributions are (a) an e ciently verifiable characterization of the unique witness for termination of the Arrival game, and (b) an e cient way of sampling from the state space of the game. We show that the problem of finding the unique witness is contained in CLS, whereas it was previously conjectured to be FPSPACE-complete. The e cient sampling procedure yields the first algorithm for the problem that has expected runtime O(cn) with c < 2.

Original languageEnglish
Title of host publication45th International Colloquium on Automata, Languages, and Programming, ICALP 2018
EditorsIoannis Chatzigiannakis , Christos Kaklamanis, Da}niel Marx, Donald Sannella
Number of pages13
PublisherSchloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing
Publication date2018
Article number60
ISBN (Electronic)9783959770767
DOIs
Publication statusPublished - 2018
Event45th International Colloquium on Automata, Languages, and Programming, ICALP 2018 - Prague, Czech Republic
Duration: 9 Jul 201813 Jul 2018

Conference

Conference45th International Colloquium on Automata, Languages, and Programming, ICALP 2018
Country/TerritoryCzech Republic
CityPrague
Period09/07/201813/07/2018
SponsorAvast, RSJ
SeriesLeibniz International Proceedings in Informatics, LIPIcs
Volume107
ISSN1868-8969

Keywords

  • CLS
  • Switch graphs
  • UP ∩ coUP
  • Zero-player game

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