论文标题

免费订单多项选择秘书的最佳算法

Optimal Algorithms for Free Order Multiple-Choice Secretary

论文作者

Hajiaghayi, Mohammad Taghi, Kowalski, Dariusz R., Krysta, Piotr, Olkowski, Jan

论文摘要

假设我们获得了整数$ k \ leq n $和$ n $ boxes标记为$ 1,\ ldots,n $由对手,每个都包含从未知分布中选择的数字。我们必须选择一个顺序打开这些盒子的订单,每当我们按照此顺序打开下一个框时,我们都会了解其号码。如果我们在盒子中拒绝一个数字,则无法召回盒子。我们的目标是接受这些数字中最大的$ k $,而不必打开所有盒子。这是免费订单多项选择秘书问题。广泛研究了秘书和先知问题的自由订单变体。 Kesselheim,Kleinberg和Niazadeh KKN(Stoc'15)针对自由订单秘书问题提起了一项对随机性有效算法的研究(在使用的随机位方面最便宜的顺序)。 我们提出了一种自由订单多项选择秘书的算法,该算法同时最适合竞争比率和使用的随机性。即,我们在具有最佳熵$θ(\ log \ log \ log n)$的订单上构建分布,以使确定性的多重阈值算法为$ 1-O(\ sqrt {\ sqrt {\ log k/k})$ - 竞争性。这以三种方式改进了KKN先前的最佳结构,其竞争比率为$ 1 -O(1/K^{1/3}) - O(1)$。我们的竞争比率(接近)是多项选择秘书问题的最佳选择。它适用于指数较大的参数$ k $;而且我们的算法是一种简单的确定性多阈值算法,而KKN中的算法是随机的。我们还证明了对多项选择秘书问题的最佳解决方案熵的相应下限,匹配我们算法的熵,在该问题上尚无这种先前的下限。 我们通过许多新技术获得了算法结果,通过这些技术,我们还可以显着改善KKN关于为经典自由订单秘书构建熵优美分布的先前结果。

Suppose we are given integer $k \leq n$ and $n$ boxes labeled $1,\ldots, n$ by an adversary, each containing a number chosen from an unknown distribution. We have to choose an order to sequentially open these boxes, and each time we open the next box in this order, we learn its number. If we reject a number in a box, the box cannot be recalled. Our goal is to accept the $k$ largest of these numbers, without necessarily opening all boxes. This is the free order multiple-choice secretary problem. Free order variants were studied extensively for the secretary and prophet problems. Kesselheim, Kleinberg, and Niazadeh KKN (STOC'15) initiated a study of randomness-efficient algorithms (with the cheapest order in terms of used random bits) for the free order secretary problems. We present an algorithm for free order multiple-choice secretary, which is simultaneously optimal for the competitive ratio and used amount of randomness. I.e., we construct a distribution on orders with optimal entropy $Θ(\log\log n)$ such that a deterministic multiple-threshold algorithm is $1-O(\sqrt{\log k/k})$-competitive. This improves in three ways the previous best construction by KKN, whose competitive ratio is $1 - O(1/k^{1/3}) - o(1)$. Our competitive ratio is (near)optimal for the multiple-choice secretary problem; it works for exponentially larger parameter $k$; and our algorithm is a simple deterministic multiple-threshold algorithm, while that in KKN is randomized. We also prove a corresponding lower bound on the entropy of optimal solutions for the multiple-choice secretary problem, matching entropy of our algorithm, where no such previous lower bound was known. We obtain our algorithmic results with a host of new techniques, and with these techniques we also improve significantly the previous results of KKN about constructing entropy-optimal distributions for the classic free order secretary.

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