When you come at the kings you best not miss
Abstract
A tournament is an orientation of a complete graph. We say that a vertex in a tournament controls another vertex if there exists a directed path of length at most two from to . 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 (SIAM J. Comput., 2003) in investigating the query complexity of finding a king, that is, the number of arcs in 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 arcs and provided a strategy that queries at most . While this upper bound has not yet been improved for the original problem, Biswas et al. (Frontiers in Algorithmics, 2017) proved that with 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 queries, we can identify a -king. To achieve this goal we use a novel structural result for tournaments.
Cite
@article{arxiv.2209.12082,
title = {When you come at the kings you best not miss},
author = {Oded Lachish and Felix Reidl and Chhaya Trehan},
journal= {arXiv preprint arXiv:2209.12082},
year = {2022}
}