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When you come at the king you best not miss

Lachish, Oded, Reidl, Felix and Trehan, Chhaya (2022) When you come at the king you best not miss. In: Dawar, Anuj and Guruswami, Venkatesan, (eds.) 42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science, FSTTCS 2022. Leibniz International Proceedings in Informatics, LIPIcs. UNSPECIFIED, 1 - 12. ISBN 9783959772617

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Identification Number: 10.4230/LIPIcs.FSTTCS.2022.25


A tournament is an orientation of a complete graph. We say that a vertex x in a tournament T ⃗ controls another vertex y if there exists a directed path of length at most two from x to y. A vertex is called a king if it controls every vertex of the tournament. It is well known that every tournament has a king. We follow Shen, Sheng, and Wu [8] in investigating the query complexity of finding a king, that is, the number of arcs in T ⃗ one has to know in order to surely identify at least one vertex as a king. The aforementioned authors showed that one always has to query at least Ω(n 4/3) arcs and provided a strategy that queries at most O(n 3/2). While this upper bound has not yet been improved for the original problem, Biswas et al. [3] proved that with O(n 4/3) queries one can identify a semi-king, meaning a vertex which controls at least half of all vertices. Our contribution is a novel strategy which improves upon the number of controlled vertices: using O(n 4/3 polylog n) queries, we can identify a (Equation presented)-king. To achieve this goal we use a novel structural result for tournaments.

Item Type: Book Section
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Additional Information: © 2022 The Author(s).
Divisions: Mathematics
Subjects: Q Science > QA Mathematics
Date Deposited: 21 Nov 2022 11:54
Last Modified: 17 Nov 2023 19:42

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