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arXiv 1602.07013cs.DS
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稠密距离图中最短路的改进界

Improved Bounds for Shortest Paths in Dense Distance Graphs

Paweł Gawrychowski, Adam Karczmarz

摘要:

我们研究了在所谓的密集距离图中计算最短路径的问题。$n$顶点上的每个平面图$G$可以被划分成一组$O(n/r)$边不相交区域(称为$r$ -划分),每个区域具有$O(r)$顶点,使得每个区域具有与其他区域共同的$O(\sqrt{r})$顶点(称为边界顶点)。一个区域的稠密距离图是一个包含其边界节点间所有对距离的完全图。$r$ -划分的稠密距离图是各个块的$O(n/r)$稠密距离图的并集。自从Fakcharoenphol和Rao引入密集距离图以来,在密集距离图中计算单源最短路径已经在基本平面图算法中找到了许多应用。Fakcharoenphol和Rao提出了一种算法(后来称为FR-Dijkstra),用于在$O\left(\frac{n}{\sqrt{r}}\log{n}\log{r}\right)$时间内计算密集距离图中的单源最短路径。我们展示了这个问题的$O\left(\frac{n}{\sqrt{r}}\left(\frac{\log^2{r}}{\log^2\log{r}}+\log{n}\log^ε{r}\right)\right)$时间算法,这是第一次改进到目前为止,FR-Dijkstra的重要情况下,$r$是多项式在$n$。在这种情况下,我们的算法是更快的一个因素的$O(\log^2{\log{n}})$,并意味着改进的上限,如多源多汇最大流,单源所有汇最大流,和(动态)精确的距离预言等平面图的问题。

英文摘要:

We study the problem of computing shortest paths in so-called dense distance graphs. Every planar graph $G$ on $n$ vertices can be partitioned into a set of $O(n/r)$ edge-disjoint regions (called an $r$-division) with $O(r)$ vertices each, such that each region has $O(\sqrt{r})$ vertices (called boundary vertices) in common with other regions. A dense distance graph of a region is a complete graph containing all-pairs distances between its boundary nodes. A dense distance graph of an $r$-division is the union of the $O(n/r)$ dense distance graphs of the individual pieces. Since the introduction of dense distance graphs by Fakcharoenphol and Rao, computing single-source shortest paths in dense distance graphs has found numerous applications in fundamental planar graph algorithms. Fakcharoenphol and Rao proposed an algorithm (later called FR-Dijkstra) for computing single-source shortest paths in a dense distance graph in $O\left(\frac{n}{\sqrt{r}}\log{n}\log{r}\right)$ time. We show an $O\left(\frac{n}{\sqrt{r}}\left(\frac{\log^2{r}}{\log^2\log{r}}+\log{n}\log^ε{r}\right)\right)$ time algorithm for this problem, which is the first improvement to date over FR-Dijkstra for the important case when $r$ is polynomial in $n$. In this case, our algorithm is faster by a factor of $O(\log^2{\log{n}})$ and implies improved upper bounds for such planar graph problems as multiple-source multiple-sink maximum flow, single-source all-sinks maximum flow, and (dynamic) exact distance oracles.

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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