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arXiv 1405.7709cs.GTcs.CC
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稳定的婚姻需要沟通

A Stable Marriage Requires Communication

Yannai A. Gonczarowski, Noam Nisan, Rafail Ostrovsky, Will Rosenbaum

摘要:

已知稳定婚姻问题的Gale-Shapley算法在最坏的情况下采取$Θ(n^2)$步骤来找到稳定的婚姻,但在平均情况下仅采取$Θ(n \log n)$步骤(具有$n$女性和$n$男性)。在1976年,克努特提出了一个问题:在一个不需要对整个输入进行顺序存取的计算模型中,最坏情况下的运行时间是否可以得到改善。Ng和Hirschberg给出了部分否定的答案,他们证明了在一个模型中需要$Θ(n^2)$查询,该模型允许参与者的偏好进行某些自然的随机访问查询。一个明显更普遍的-虽然稍微弱-下限来自西格尔的通信复杂性的一般分析,即需要$Ω(n^2)$布尔查询,以找到一个稳定的婚姻,无论允许的布尔查询集。使用减少通信的不相交问题通信复杂性性,我们给出了一个更简单,但显着更强大的参数表明,$Ω(n^2)$布尔查询的任何类型的确实需要找到一个稳定的-甚至是一个近似稳定的-婚姻。值得注意的是,与西格尔的下限不同,我们的下限也推广到(A)随机算法,(B)允许对女性偏好简档和男性偏好简档进行任意单独的预处理,(C)基本问题的几个变体,例如给定的一对是否在每个/一些稳定的婚姻中结婚,以及(D)确定拟议的婚姻是稳定的还是远不稳定的。为了分析“近似稳定”婚姻,我们引入了“稳定距离”的概念,并提供了一个有效的算法计算。

英文摘要:

The Gale-Shapley algorithm for the Stable Marriage Problem is known to take $Θ(n^2)$ steps to find a stable marriage in the worst case, but only $Θ(n \log n)$ steps in the average case (with $n$ women and $n$ men). In 1976, Knuth asked whether the worst-case running time can be improved in a model of computation that does not require sequential access to the whole input. A partial negative answer was given by Ng and Hirschberg, who showed that $Θ(n^2)$ queries are required in a model that allows certain natural random-access queries to the participants' preferences. A significantly more general - albeit slightly weaker - lower bound follows from Segal's general analysis of communication complexity, namely that $Ω(n^2)$ Boolean queries are required in order to find a stable marriage, regardless of the set of allowed Boolean queries. Using a reduction to the communication complexity of the disjointness problem, we give a far simpler, yet significantly more powerful argument showing that $Ω(n^2)$ Boolean queries of any type are indeed required for finding a stable - or even an approximately stable - marriage. Notably, unlike Segal's lower bound, our lower bound generalizes also to (A) randomized algorithms, (B) allowing arbitrary separate preprocessing of the women's preferences profile and of the men's preferences profile, (C) several variants of the basic problem, such as whether a given pair is married in every/some stable marriage, and (D) determining whether a proposed marriage is stable or far from stable. In order to analyze "approximately stable" marriages, we introduce the notion of "distance to stability" and provide an efficient algorithm for its computation.

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