,
Shivesh K. Roy
Creative Commons Attribution 4.0 International license
We study a new graph separation problem called Multiway Near-Separator. Given an undirected graph G, integer k, and terminal set T ⊆ V(G), it asks whether there is a vertex set S ⊆ V(G) ⧵ T of size at most k such that in graph G-S, no pair of distinct terminals can be connected by two pairwise internally vertex-disjoint paths. Hence each terminal pair can be separated in G-S by removing at most one vertex. The problem is therefore a generalization of (Node) Multiway Cut, which asks for a vertex set for which each terminal is in a different component of G-S. We develop a fixed-parameter tractable algorithm for Multiway Near-Separator running in time 2^{𝒪(k log k)} ⋅ n^{𝒪(1)}. Our algorithm is based on a new pushing lemma for solutions with respect to important separators, along with two problem-specific ingredients. The first is a polynomial-time subroutine to reduce the number of terminals in the instance to a polynomial in the solution size k plus the size of a given suboptimal solution. The second is a polynomial-time algorithm that, given a graph G and terminal set T ⊆ V(G) along with a single vertex x ∈ V(G) that forms a multiway near-separator, computes a 14-approximation for the problem of finding a multiway near-separator not containing x.
@InProceedings{jansen_et_al:LIPIcs.IPEC.2023.28,
author = {Jansen, Bart M. P. and Roy, Shivesh K.},
title = {{On the Parameterized Complexity of Multiway Near-Separator}},
booktitle = {18th International Symposium on Parameterized and Exact Computation (IPEC 2023)},
pages = {28:1--28:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-305-8},
ISSN = {1868-8969},
year = {2023},
volume = {285},
editor = {Misra, Neeldhara and Wahlstr\"{o}m, Magnus},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2023.28},
URN = {urn:nbn:de:0030-drops-194470},
doi = {10.4230/LIPIcs.IPEC.2023.28},
annote = {Keywords: fixed-parameter tractability, multiway cut, near-separator}
}