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O(log n)-Approximation Algorithms for Bipartiteness Ratio

2025/07/17 by Tasuku Soma, Soma, Tasuku, Mingquan Ye +3
Computer Science · Decision Sciences · #Advanced Graph Theory Research #Optimization and Search Problems #Game Theory and Applications

paper · pdf · doi:10.48550/arxiv.2507.12847

Abstract

We propose an O(log n)-approximation algorithm for the bipartiteness ratio of undirected graphs introduced by Trevisan (SIAM Journal on Computing, vol. 41, no. 6, 2012), where n is the number of vertices. Our approach extends the cut-matching game framework for sparsest cut to the bipartiteness ratio, and requires only \mathoppolylog n many single-commodity undirected maximum flow computations. Therefore, with the current fastest undirected max-flow algorithms, it runs in almost linear time. Along the way, we introduce the concept of well-linkedness for skew-symmetric graphs and prove a novel characterization of bipartiteness ratio in terms of well-linkedness in an auxiliary skew-symmetric graph, which may be of independent interest. As an application, we devise an O(mn)-time algorithm for the minimum uncut problem: given a graph whose optimal cut leaves an η fraction of edges uncut, we find a cut that leaves only an O(log n log(1/η)) ⋅ η fraction of edges uncut, where m is the number of edges. Finally, we propose a directed analogue of the bipartiteness ratio, and we give a polynomial-time algorithm that achieves an O(log n) approximation for this measure via a directed Leighton--Rao-style embedding. We also propose an algorithm for the minimum directed uncut problem with a guarantee similar to that for the minimum uncut problem.

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