Abstract
A general instance of a Degree-Constrained Subgraph problem consists of an edge-weighted or vertex-weighted graph G and the objective is to find an optimal weighted subgraph, subject to certain degree constraints on the vertices of the subgraph. This paper considers two natural Degree-Constrained Subgraph problems and studies their behavior in terms of approximation algorithms. These problems take as input an undirected graph G = (V,E), with |V| = n and |E| = m. Our results, together with the definition of the two problems, are listed below.
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The Maximum Degree-Bounded Connected Subgraph problem (MDBCS d ) takes as input a weight function \(\omega : E \rightarrow \mathbb R^+\) and an integer d ≥ 2, and asks for a subset E′ ⊆ E such that the subgraph G′ = (V,E′) is connected, has maximum degree at most d, and ∑ e ∈ E′ ω(e) is maximized. This problem is one of the classical NP-hard problems listed by Garey and Johnson in [Computers and Intractability, W.H. Freeman, 1979], but there were no results in the literature except for d = 2. We prove that MDBCS d is not in Apx for any d ≥ 2 (this was known only for d = 2) and we provide a \((\min \{m/ \log n,\ nd/(2 \log n)\})\)-approximation algorithm for unweighted graphs, and a \((\min\{n/2,\ m/d\})\)-approximation algorithm for weighted graphs. We also prove that when G has a low-degree spanning tree, in terms of d, MDBCS d can be approximated within a small constant factor in unweighted graphs.
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The Minimum Subgraph of Minimum Degree ≥ d (MSMD d ) problem requires finding a smallest subgraph of G (in terms of number of vertices) with minimum degree at least d. We prove that MSMD d is not in Apx for any d ≥ 3 and we provide an \(\mathcal{O}(n/\log n)\)-approximation algorithm for the class of graphs excluding a fixed graph as a minor, using dynamic programming techniques and a known structural result on graph minors.
This work has been partially supported by European project IST FET AEOLUS, PACA region of France, Ministerio de Educación y Ciencia of Spain, European Regional Development Fund under project TEC2005-03575, Catalan Research Council under project 2005SGR00256 and COST action 293 GRAAL, and has been done in the context of the crc Corso with France Telecom.
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Amini, O., Peleg, D., Pérennes, S., Sau, I., Saurabh, S. (2009). Degree-Constrained Subgraph Problems: Hardness and Approximation Results. In: Bampis, E., Skutella, M. (eds) Approximation and Online Algorithms. WAOA 2008. Lecture Notes in Computer Science, vol 5426. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-93980-1_3
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