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arXiv 2602.07394cs.DS
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扩展图上的最小生成树的局部计算算法

Local Computation Algorithms for (Minimum) Spanning Trees on Expander Graphs

School of Computer Science and Technology, University of Science and Technology of China(中国科学技术大学计算机科学与技术学院)

Pan Peng, Yuyang Wang

AI总结:

本文提出了一种针对扩展图的局部计算算法,用于构造生成树和最小生成树,实现了子线性时间复杂度的高效算法。

摘要:

我们研究了构造生成树的局部计算算法(LCAs)。在这种设置中,目标是局部确定,对于每条边e∈E,它是否属于输入图G的生成树T,其中T由G和算法的随机性隐式定义。已知在一般图中,生成树的LCAs并不存在,即使对于简单的图家族也是如此。我们识别出一个自然且广泛研究的图类——扩展图——确实允许生成树的子线性时间LCAs。这可能令人惊讶,因为之前关于扩展图的研究只成功设计了稀疏生成子图的LCAs,而不是完整的生成树。我们设计了一个具有探测复杂度O(√n(log²n/ϕ² + d))的LCA,适用于导数至少为ϕ且最大度数至多为d(不一定为常数)的图。当ϕ和d为常数时,这几乎是最优的,因为即使对于扩展图,Ω(√n)次探测也是必需的。接下来,我们证明对于自然类的ER图G(n,p),其中np = n^δ对于任何常数δ>0(这些图以高概率是扩展图),√n下限可以被绕过。具体来说,我们为这类图提供了一个平均情况的LCA,其探测复杂度为O(√n^{1-δ})。最后,我们将我们的技术扩展到设计加权扩展图上的最小生成树(MST)问题的LCAs。具体来说,给定一个d-正则无权图Ḡ,其具有足够的扩展性,我们考虑通过为每条边分配独立且均匀的随机权重从{1,…,W}得到加权图G,其中W = O(d)。我们证明存在一个与G的精确MST一致的LCA,其探测复杂度为O(√n d²)。

英文摘要:

We study \emph{local computation algorithms (LCAs)} for constructing spanning trees. In this setting, the goal is to locally determine, for each edge $ e \in E $, whether it belongs to a spanning tree $ T $ of the input graph $ G $, where $ T $ is defined implicitly by $ G $ and the randomness of the algorithm. It is known that LCAs for spanning trees do not exist in general graphs, even for simple graph families. We identify a natural and well-studied class of graphs -- \emph{expander graphs} -- that do admit \emph{sublinear-time} LCAs for spanning trees. This is perhaps surprising, as previous work on expanders only succeeded in designing LCAs for \emph{sparse spanning subgraphs}, rather than full spanning trees. We design an LCA with probe complexity $ O\left(\sqrt{n}\left(\frac{\log^2 n}{ϕ^2} + d\right)\right)$ for graphs with conductance at least $ ϕ$ and maximum degree at most $ d $ (not necessarily constant), which is nearly optimal when $ϕ$ and $d$ are constants, since $Ω(\sqrt{n})$ probes are necessary even for expanders. Next, we show that for the natural class of \emph{\ER graphs} $ G(n, p) $ with $ np = n^δ $ for any constant $ δ> 0 $ (which are expanders with high probability), the $ \sqrt{n} $ lower bound can be bypassed. Specifically, we give an \emph{average-case} LCA for such graphs with probe complexity $ \tilde{O}(\sqrt{n^{1 - δ}})$. Finally, we extend our techniques to design LCAs for the \emph{minimum spanning tree (MST)} problem on weighted expander graphs. Specifically, given a $d$-regular unweighted graph $\bar{G}$ with sufficiently strong expansion, we consider the weighted graph $G$ obtained by assigning to each edge an independent and uniform random weight from $\{1,\ldots,W\}$, where $W = O(d)$. We show that there exists an LCA that is consistent with an exact MST of $G$, with probe complexity $\tilde{O}(\sqrt{n}d^2)$.

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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