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arXiv 1408.7033cs.DS
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一类在线困难问题的建议复杂性

The Advice Complexity of a Class of Hard Online Problems

Joan Boyar, Lene M. Favrholdt, Christian Kudahl, Jesper W. Mikkelsen

摘要:

在线问题的建议复杂度是衡量在线算法需要多少未来知识才能达到一定的竞争比的指标。使用建议复杂度,我们定义了第一个在线复杂度类AOC。这类问题包括独立集、顶点覆盖、支配集和其他几个完全问题。AOC完全问题是困难的,因为在线算法的一个错误答案可能会产生毁灭性的后果。对于这些问题中的每一个,我们表明,$\log\left(1+(c-1)^{c-1}/c^{c}\right)n=Θ(n/c)$位的意见是必要的和足够的(添加剂项$O(\log n)$),以实现竞争比$c$。这些结果是通过引入一个与Emek et al.(TCS 2011)和Böckenhauer et al.(TCS 2014)相关的新的字符串猜测问题获得的。事实证明,这给出了一个强大但易于使用的方法,用于提供整个在线问题(AOC完全问题)的建议复杂性的上限和下限。Halldórsson等人(TCS 2002)在相关模型中关于在线独立集的先前结果暗示问题的建议复杂度为$Θ(n/c)$。我们的结果改进了这一点,提供了一个精确的公式为高阶项。对于在线不相交路径分配,Böckenhauer等人(ISAAC 2009)给出了建议复杂度的$Ω(n/c)$下限和$O((n\log c)/c)$上限。我们将上界改进了$\log c$倍。对于其余的问题,没有限制他们的建议复杂性是以前已知的。

英文摘要:

The advice complexity of an online problem is a measure of how much knowledge of the future an online algorithm needs in order to achieve a certain competitive ratio. Using advice complexity, we define the first online complexity class, AOC. The class includes independent set, vertex cover, dominating set, and several others as complete problems. AOC-complete problems are hard, since a single wrong answer by the online algorithm can have devastating consequences. For each of these problems, we show that $\log\left(1+(c-1)^{c-1}/c^{c}\right)n=Θ(n/c)$ bits of advice are necessary and sufficient (up to an additive term of $O(\log n)$) to achieve a competitive ratio of $c$. The results are obtained by introducing a new string guessing problem related to those of Emek et al. (TCS 2011) and Böckenhauer et al. (TCS 2014). It turns out that this gives a powerful but easy-to-use method for providing both upper and lower bounds on the advice complexity of an entire class of online problems, the AOC-complete problems. Previous results of Halldórsson et al. (TCS 2002) on online independent set, in a related model, imply that the advice complexity of the problem is $Θ(n/c)$. Our results improve on this by providing an exact formula for the higher-order term. For online disjoint path allocation, Böckenhauer et al. (ISAAC 2009) gave a lower bound of $Ω(n/c)$ and an upper bound of $O((n\log c)/c)$ on the advice complexity. We improve on the upper bound by a factor of $\log c$. For the remaining problems, no bounds on their advice complexity were previously known.

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