Given an undirected graph on n vertices with weights on its edges, Min WCF(p) consists of computing a covering forest of minimum weight such that each of its tree components contains at least p vertices. It has been proved that Min WCF(p) is NP-hard for any p≥4 (Imielinska et al., 1993) but -approximable (Goemans and Williamson, 1995). While Min WCF(2) is polynomial-time solvable, already the unweighted version of Min WCF(3) is NP-hard even on planar bipartite graphs of maximum degree 3. We prove here that for any p≥4, the unweighted version is NP-hard, even for planar bipartite graphs of maximum degree 3; moreover, the unweighted version for any p≥3 has no ptas for bipartite graphs of maximum degree 3. The latter theorem is the first-ever APX-hardness result on this problem. On the other hand, we show that Min WCF(p) is polynomial-time solvable on graphs with bounded treewidth, and for any p bounded by it has a ptas on planar graphs. © 2009 Springer-Verlag Berlin Heidelberg.
CITATION STYLE
Bazgan, C., Couëtoux, B., & Tuza, Z. (2009). Covering a graph with a constrained forest. In Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) (Vol. 5878 LNCS, pp. 892–901). Springer Verlag. https://doi.org/10.1007/978-3-642-10631-6_90
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