In the Minimum Consistent Subset (MCS) problem, we are presented with a connected simple undirected graph G, consisting of a vertex set V(G) of size n and an edge set E(G). Each vertex in V(G) is assigned a color from the set {1,2,…, c}. The objective is to determine a subset V' ⊆ V(G) with minimum possible cardinality, such that for every vertex v ∈ V(G), at least one of its nearest neighbors in V' (measured in terms of the hop distance) shares the same color as v. The decision problem, indicating whether there exists a subset V' of cardinality at most l for some positive integer l, is known to be NP-complete even for planar graphs. In this paper, we establish that the MCS problem is NP-complete on trees. We also provide a fixed-parameter tractable (FPT) algorithm for MCS on trees parameterized by the number of colors (c) running in O(2^{6c} n^6) time, significantly improving the currently best-known algorithm whose running time is O(2^{4c} n^{2c+3}). In an effort to comprehensively understand the computational complexity of the MCS problem across different graph classes, we extend our investigation to interval graphs. We show that it remains NP-complete for interval graphs, thus enriching graph classes where MCS remains intractable.
@InProceedings{banik_et_al:LIPIcs.FSTTCS.2024.7, author = {Banik, Aritra and Das, Sayani and Maheshwari, Anil and Manna, Bubai and Nandy, Subhas C. and Priya K. M., Krishna and Roy, Bodhayan and Roy, Sasanka and Sahu, Abhishek}, title = {{Minimum Consistent Subset in Trees and Interval Graphs}}, booktitle = {44th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2024)}, pages = {7:1--7:15}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-355-3}, ISSN = {1868-8969}, year = {2024}, volume = {323}, editor = {Barman, Siddharth and Lasota, S{\l}awomir}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2024.7}, URN = {urn:nbn:de:0030-drops-221960}, doi = {10.4230/LIPIcs.FSTTCS.2024.7}, annote = {Keywords: Nearest-Neighbor Classification, Minimum Consistent Subset, Trees, Interval Graphs, Parameterized complexity, NP-complete} }
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