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Online Sorting and Online TSP: Randomized, Stochastic, and High-Dimensional
University of Copenhagen, Denmark.
KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.ORCID iD: 0000-0001-8430-2441
University of California, Santa Cruz, CA, USA.
University of Copenhagen, Denmark.
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2024 (English)In: 32nd Annual European Symposium on Algorithms, ESA 2024, Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing , 2024, article id 5Conference paper, Published paper (Refereed)
Abstract [en]

In the online sorting problem, n items are revealed one by one and have to be placed (immediately and irrevocably) into empty cells of a size-n array. The goal is to minimize the sum of absolute differences between items in consecutive cells. This natural problem was recently introduced by Aamand, Abrahamsen, Beretta, and Kleist (SODA 2023) as a tool in their study of online geometric packing problems. They showed that when the items are reals from the interval [0, 1] a competitive ratio of O(√n) is achievable, and no deterministic algorithm can improve this ratio asymptotically. In this paper, we extend and generalize the study of online sorting in three directions: randomized: we settle the open question of Aamand et al. by showing that the O(√n) competitive ratio for the online sorting of reals cannot be improved even with the use of randomness; stochastic: we consider inputs consisting of n samples drawn uniformly at random from an interval, and give an algorithm with an improved competitive ratio of Oe(n1/4). The result reveals connections between online sorting and the design of efficient hash tables; high-dimensional: we show that Oe(√n)-competitive online sorting is possible even for items from Rd, for arbitrary fixed d, in an adversarial model. This can be viewed as an online variant of the classical TSP problem where tasks (cities to visit) are revealed one by one and the salesperson assigns each task (immediately and irrevocably) to its timeslot. Along the way, we also show a tight O(log n)-competitiveness result for uniform metrics, i.e., where items are of different types and the goal is to order them so as to minimize the number of switches between consecutive items of different types.

Place, publisher, year, edition, pages
Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing , 2024. article id 5
Keywords [en]
online algorithm, sorting, TSP
National Category
Computer Sciences Probability Theory and Statistics
Identifiers
URN: urn:nbn:se:kth:diva-354913DOI: 10.4230/LIPIcs.ESA.2024.5Scopus ID: 2-s2.0-85205739848OAI: oai:DiVA.org:kth-354913DiVA, id: diva2:1906243
Conference
32nd Annual European Symposium on Algorithms, ESA 2024, London, United Kingdom of Great Britain and Northern Ireland, Sep 2 2024 - Sep 4 2024
Note

QC 20241018

 Part of ISBN 9783959773386

Available from: 2024-10-16 Created: 2024-10-16 Last updated: 2024-10-18Bibliographically approved

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Bercea, Ioana

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