{"title":"当你攻击国王时,最好不要失手","authors":"Oded Lachish, F. Reidl, Chhaya Trehan","doi":"10.48550/arXiv.2209.12082","DOIUrl":null,"url":null,"abstract":"A tournament is an orientation of a complete graph. We say that a vertex $x$ in a tournament $\\vec T$ 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 (SIAM J. Comput., 2003) in investigating the query complexity of finding a king, that is, the number of arcs in $\\vec T$ 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 $\\Omega(n^{4/3})$ 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. (Frontiers in Algorithmics, 2017) 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 $O(n^{4/3} \\operatorname{polylog} n)$ queries, we can identify a $(\\frac{1}{2}+\\frac{2}{17})$-king. To achieve this goal we use a novel structural result for tournaments.","PeriodicalId":175000,"journal":{"name":"Foundations of Software Technology and Theoretical Computer Science","volume":"12 1","pages":"0"},"PeriodicalIF":0.0000,"publicationDate":"2022-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"1","resultStr":"{\"title\":\"When you come at the kings you best not miss\",\"authors\":\"Oded Lachish, F. Reidl, Chhaya Trehan\",\"doi\":\"10.48550/arXiv.2209.12082\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"A tournament is an orientation of a complete graph. We say that a vertex $x$ in a tournament $\\\\vec T$ 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 (SIAM J. Comput., 2003) in investigating the query complexity of finding a king, that is, the number of arcs in $\\\\vec T$ 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 $\\\\Omega(n^{4/3})$ 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. (Frontiers in Algorithmics, 2017) 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 $O(n^{4/3} \\\\operatorname{polylog} n)$ queries, we can identify a $(\\\\frac{1}{2}+\\\\frac{2}{17})$-king. To achieve this goal we use a novel structural result for tournaments.\",\"PeriodicalId\":175000,\"journal\":{\"name\":\"Foundations of Software Technology and Theoretical Computer Science\",\"volume\":\"12 1\",\"pages\":\"0\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"2022-09-24\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"1\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Foundations of Software Technology and Theoretical Computer Science\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/10.48550/arXiv.2209.12082\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Foundations of Software Technology and Theoretical Computer Science","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.48550/arXiv.2209.12082","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 1
摘要
比武是完全图的一个方向。如果存在一条从$x$到$y$长度不超过2的有向路径,我们就说锦标赛中的顶点$x$$\vec T$控制另一个顶点$y$。如果一个顶点控制了比赛的每个顶点,那么它就被称为国王。众所周知,每次比赛都有一个国王。我们跟随沈、盛和吴(SIAM J. Comput)。(2003)在研究寻找国王的查询复杂性时,即,为了确定至少有一个顶点是国王,必须知道$\vec T$中弧的数量。前面提到的作者表明,人们总是必须查询至少$\Omega(n^{4/3})$弧线,并提供了最多查询$O(n^{3/2})$的策略。虽然这个上限尚未对原始问题进行改进,但Biswas等人(Frontiers in Algorithmics, 2017)证明,使用$O(n^{4/3})$查询可以识别半王,即控制至少一半顶点的顶点。我们的贡献是一种新的策略,它改进了控制顶点的数量:使用$O(n^{4/3} \operatorname{polylog} n)$查询,我们可以识别一个$(\frac{1}{2}+\frac{2}{17})$ -king。为了实现这一目标,我们在比赛中使用了一种新颖的结构结果。
A tournament is an orientation of a complete graph. We say that a vertex $x$ in a tournament $\vec T$ 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 (SIAM J. Comput., 2003) in investigating the query complexity of finding a king, that is, the number of arcs in $\vec T$ 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 $\Omega(n^{4/3})$ 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. (Frontiers in Algorithmics, 2017) 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 $O(n^{4/3} \operatorname{polylog} n)$ queries, we can identify a $(\frac{1}{2}+\frac{2}{17})$-king. To achieve this goal we use a novel structural result for tournaments.