Faster algorithms for all-pairs bounded min-cuts

A Abboud, L Georgiadis, GF Italiano… - arXiv preprint arXiv …, 2018 - arxiv.org
arXiv preprint arXiv:1807.05803, 2018arxiv.org
The All-Pairs Min-Cut problem (aka All-Pairs Max-Flow) asks to compute a minimum $ s $-$ t
$ cut (or just its value) for all pairs of vertices $ s, t $. We study this problem in directed
graphs with unit edge/vertex capacities (corresponding to edge/vertex connectivity). Our
focus is on the $ k $-bounded case, where the algorithm has to find all pairs with min-cut
value less than $ k $, and report only those. The most basic case $ k= 1$ is the Transitive
Closure (TC) problem, which can be solved in graphs with $ n $ vertices and $ m $ edges in …
The All-Pairs Min-Cut problem (aka All-Pairs Max-Flow) asks to compute a minimum - cut (or just its value) for all pairs of vertices . We study this problem in directed graphs with unit edge/vertex capacities (corresponding to edge/vertex connectivity). Our focus is on the -bounded case, where the algorithm has to find all pairs with min-cut value less than , and report only those. The most basic case is the Transitive Closure (TC) problem, which can be solved in graphs with vertices and edges in time combinatorially, and in time where is the matrix-multiplication exponent. These time bounds are conjectured to be optimal. We present new algorithms and conditional lower bounds that advance the frontier for larger , as follows: (i) A randomized algorithm for vertex capacities that runs in time . (ii) Two deterministic algorithms for edge capacities (which is more general) that work in DAGs and further reports a minimum cut for each pair. The first algorithm is combinatorial (does not involve matrix multiplication) and runs in time . The second algorithm can be faster on dense DAGs and runs in time . (iii) The first super-cubic lower bound of time under the -Clique conjecture, which holds even in the simplest case of DAGs with unit vertex capacities. It improves on the previous (SETH-based) lower bounds even in the unbounded setting . For combinatorial algorithms, our reduction implies an conditional lower bound. Thus, we identify new settings where the complexity of the problem is (conditionally) higher than that of TC.
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