改进的结构和几何集合系统的在线击中集算法
Improved Online Hitting Set Algorithms for Structured and Geometric Set Systems
AI总结:
本文提出一种O(logn loglogn)的竞争算法,用于解决具有线性浅单元复杂度的集合系统的加权在线击中集问题,突破了通用情况下的双重对数障碍。
摘要:
在在线击中集问题中,集合随时间到达,算法必须维护一个元素子集,以击中所有已见过的集合。Alon等人(SICOMP 2009)给出了一个具有O(logn logm)竞争比的算法,用于一般的在线击中集和集合覆盖问题,对于m个集合和n个元素。已知该结果对于高效的在线算法来说是最佳的。鉴于这一障碍,我们提出问题:能否在结构和几何集合系统上打破这一双重对数现象?我们为具有线性浅单元复杂度的集合系统的加权在线击中集问题提供了O(logn loglogn)的竞争算法,将一般结果中的双重对数因子替换为一个单个对数项。我们的结果导致了对自然几何集合族的加权在线击中集问题的首个界,从而回答了关于一般和几何加权在线击中集问题之间差距的开放问题。
英文摘要:
In the online hitting set problem, sets arrive over time, and the algorithm has to maintain a subset of elements that hit all the sets seen so far. Alon, Awerbuch, Azar, Buchbinder, and Naor (SICOMP 2009) gave an algorithm with competitive ratio $O(\log n \log m)$ for the (general) online hitting set and set cover problems for $m$ sets and $n$ elements; this is known to be tight for efficient online algorithms. Given this barrier for general set systems, we ask: can we break this double-logarithmic phenomenon for online hitting set/set cover on structured and geometric set systems? We provide an $O(\log n \log\log n)$-competitive algorithm for the weighted online hitting set problem on set systems with linear shallow-cell complexity, replacing the double-logarithmic factor in the general result by effectively a single logarithmic term. As a consequence of our results we obtain the first bounds for weighted online hitting set for natural geometric set families, thereby answering open questions regarding the gap between general and geometric weighted online hitting set problems.
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