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Multicuts in Unweighted Graphs and Digraphs with Bounded Degree and Bounded Tree-Width

By Gruia Calinescu, Cristina G. Fernandes and Bruce Reed


The Multicut problem can be defined as: given a graph G and a collection of pairs of distinct vertices (s i , t i ) of G, find a minimum set of edges of G whose removal disconnects each s i from the corresponding t i . Multicut is known to be NP-hard and Max SNP-hard even when the input graph is restricted to being a tree. The main result of the paper is a polynomial-time approximation scheme (PTAS) for Multicut in unweighted graphs with bounded degree and bounded tree-width. That is, for any # > 0, we present a polynomial-time (1 + #)-approximation algorithm. In the particular case when the input is a bounded-degree tree, we have a linear-time implementation of the algorithm. We also provide some hardness results: we prove that Multicut is still NP-hard for binary trees and that it is Max SNP-hard if we drop any of the three conditions (unweighted, bounded-degree, bounded tree-width). Finally we show that some of these results extend to the vertex version of Multicut and to a..

Year: 1998
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