论文标题

通过公平削减的近距离时间近似

Near-Linear Time Approximations for Cut Problems via Fair Cuts

论文作者

Li, Jason, Nanongkai, Danupon, Panigrahi, Debmalya, Saranurak, Thatchaphol

论文摘要

我们介绍了{\ em fair cuts}的概念,作为一种方法,以利用无方向图中的大约$(s,t)$ - mincut(等效于$(s,t)$ - maxflow)算法,以获取几个切割问题的接近线性时间近似算法。对于任何$α\ geq 1 $,$α$ - fair $(s,t)$ - 切割是$(s,t)$ - 剪切,因此存在$(s,t)$ - 流量使用$ 1/α$的容量\ emph {emph {emph {emph {emph {emph {emph {avery)。 (因此,任何$α$ fair削减也是一个$α$ - 适当的mincut,但反之亦然。)我们给出了$(1+ε)$ - 公平$(s,t)$的算法 - $ \ tilde {o \ tilde {o}(o}(o}(m)$ - time,以$($)的运行时间,以$($)$($($)$($) - [Peng,Soda '16]。然后,我们通过证明该结果几乎立即导致多个应用来证明这种方法的力量: - 第一个接近线性的时间$(1+ε)$ - 近似算法,该算法计算All Pairs MaxFlow值(通过构造近似的Gomory-Hu树)。在我们工作之前,即使是因为斯坦纳·米库特(Steiner Mincut)的特殊情况[迪尼茨(Dinitz)和瓦恩斯坦(Vainstein),斯托克(Stoc '94),这一结果也不为人所知。 Cole和Hariharan,Stoc '03]; - 用于计算$(1+ε)$ - 近对的maxflow值(再次通过近似Gomory-hu树)计算$(1+ε)$ - 近似值的第一个几乎是线性工作的子多项式深度算法; - 即使膨胀参数在多项式较小的情况下,也有效的第一个近线性时间扩展算法;这涵盖了以前无与伦比的算法[Nanongkai和Saranurak,Focs '17; Wulff-Nilsen,Focs '17; Saranurak和Wang,Soda '19]。

We introduce the notion of {\em fair cuts} as an approach to leverage approximate $(s,t)$-mincut (equivalently $(s,t)$-maxflow) algorithms in undirected graphs to obtain near-linear time approximation algorithms for several cut problems. Informally, for any $α\geq 1$, an $α$-fair $(s,t)$-cut is an $(s,t)$-cut such that there exists an $(s,t)$-flow that uses $1/α$ fraction of the capacity of \emph{every} edge in the cut. (So, any $α$-fair cut is also an $α$-approximate mincut, but not vice-versa.) We give an algorithm for $(1+ε)$-fair $(s,t)$-cut in $\tilde{O}(m)$-time, thereby matching the best runtime for $(1+ε)$-approximate $(s,t)$-mincut [Peng, SODA '16]. We then demonstrate the power of this approach by showing that this result almost immediately leads to several applications: - the first nearly-linear time $(1+ε)$-approximation algorithm that computes all-pairs maxflow values (by constructing an approximate Gomory-Hu tree). Prior to our work, such a result was not known even for the special case of Steiner mincut [Dinitz and Vainstein, STOC '94; Cole and Hariharan, STOC '03]; - the first almost-linear-work subpolynomial-depth parallel algorithms for computing $(1+ε)$-approximations for all-pairs maxflow values (again via an approximate Gomory-Hu tree) in unweighted graphs; - the first near-linear time expander decomposition algorithm that works even when the expansion parameter is polynomially small; this subsumes previous incomparable algorithms [Nanongkai and Saranurak, FOCS '17; Wulff-Nilsen, FOCS '17; Saranurak and Wang, SODA '19].

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