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arXiv 1603.04892cs.DS
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二叉搜索树的边界景观

The landscape of bounds for binary search trees

Parinya Chalermsook, Mayank Goswami, László Kozma, Kurt Mehlhorn, Thatchaphol Saranurak

摘要:

具有旋转的二叉搜索树(BST)可以适应搜索序列中的各种结构,实现比Theta(log n)最坏情况保证更好的摊销访问时间。结构属性的经典例子包括静态最优性,顺序存取,工作集,键独立最优性,和动态手指,所有这些都是现在已知的两个著名的在线BST算法(Splay和Greedy)实现。(...)在本文中,我们介绍了新的属性,解释效率的序列没有捕获的任何以前已知的属性,并提供了新的障碍,动态最优猜想。我们还在各种新旧物业之间建立联系。例如,我们显示以下内容。(i)对于d-可分解序列,贪婪代价的紧界为O(n log d)。该结果基于Iacono和Langerman最近的懒惰手指结果(SODA 2016)。另一方面,我们表明,懒惰的手指不能单独解释的效率模式避免序列,即使在一些最简单的情况下。(ii)使用多个懒惰手指的边界层次结构,解决了Iacono和Langerman最近的问题。(iii)Iacono(Mammica 2005)介绍的键独立设置中Move-to-root启发式的最优性。(iv)一种新的工具,允许组合任何有限数量的声音结构属性。作为一个应用程序,我们展示了一类序列的成本上界,所有已知的属性无法捕捉。(v)两类BST性质之间的等价性。这种连接所基于的观察是已知的-我们使其明确,并将其应用于经典的BST属性。(...)

英文摘要:

Binary search trees (BSTs) with rotations can adapt to various kinds of structure in search sequences, achieving amortized access times substantially better than the Theta(log n) worst-case guarantee. Classical examples of structural properties include static optimality, sequential access, working set, key-independent optimality, and dynamic finger, all of which are now known to be achieved by the two famous online BST algorithms (Splay and Greedy). (...) In this paper, we introduce novel properties that explain the efficiency of sequences not captured by any of the previously known properties, and which provide new barriers to the dynamic optimality conjecture. We also establish connections between various properties, old and new. For instance, we show the following. (i) A tight bound of O(n log d) on the cost of Greedy for d-decomposable sequences. The result builds on the recent lazy finger result of Iacono and Langerman (SODA 2016). On the other hand, we show that lazy finger alone cannot explain the efficiency of pattern avoiding sequences even in some of the simplest cases. (ii) A hierarchy of bounds using multiple lazy fingers, addressing a recent question of Iacono and Langerman. (iii) The optimality of the Move-to-root heuristic in the key-independent setting introduced by Iacono (Algorithmica 2005). (iv) A new tool that allows combining any finite number of sound structural properties. As an application, we show an upper bound on the cost of a class of sequences that all known properties fail to capture. (v) The equivalence between two families of BST properties. The observation on which this connection is based was known before - we make it explicit, and apply it to classical BST properties. (...)

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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