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There has been recent progress in showing that the exponential dependence on treewidth in dynamic programming algorithms for solving NP-hard problems is optimal under the Strong Exponential Time Hypothesis (SETH). We extend this work to r-domination problems. In r-dominating set, one wishes to find a minimum subset S of vertices such that every vertex of G is within r hops of some vertex in S. In connected r-dominating set, one additionally requires that the set induces a connected subgraph of G. We give a O((2r+1)^tw n) time algorithm for r-dominating set and a randomized O((2r+2)^tw n^{O(1)}) time algorithm for connected r-dominating set in n-vertex graphs of treewidth tw. We show that the running time dependence on r and tw is the best possible under SETH. This adds to earlier observations that a "+1" in the denominator is required for connectivity constraints.
@InProceedings{borradaile_et_al:LIPIcs.IPEC.2016.8,
author = {Borradaile, Glencora and Le, Hung},
title = {{Optimal Dynamic Program for r-Domination Problems over Tree Decompositions}},
booktitle = {11th International Symposium on Parameterized and Exact Computation (IPEC 2016)},
pages = {8:1--8:23},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-023-1},
ISSN = {1868-8969},
year = {2017},
volume = {63},
editor = {Guo, Jiong and Hermelin, Danny},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2016.8},
URN = {urn:nbn:de:0030-drops-69199},
doi = {10.4230/LIPIcs.IPEC.2016.8},
annote = {Keywords: r-dominating set, Exponential Time Hypothesis, Dynamic Programming}
}