,
Alexander Firbas
,
Robert Ganian
,
Hung P. Hoang
,
Krisztina Szilágyi
Creative Commons Attribution 4.0 International license
We investigate the computation of minimum-cost spanning trees satisfying prescribed vertex degree constraints: Given a graph G and a constraint function D, we ask for a (minimum-cost) spanning tree T such that for each vertex v, T achieves a degree specified by D(v). Specifically, we consider three kinds of constraint functions ordered by their generality - D may either assign to each vertex a list of admissible degrees, an upper bound on the degree, or a specific degree. Using a combination of novel techniques and state-of-the-art machinery, we obtain an almost-complete overview of the fine-grained complexity of these problems taking into account the most classical structural graph parameters of the input graph G. In particular, we present SETH-tight upper and lower bounds for these problems when parameterized by pathwidth and cutwidth, an ETH-tight algorithm parameterized by clique-width, and a nearly SETH-tight algorithm parameterized by treewidth. In order to obtain our upper bound for clique-width, we develop a novel technique of double representation through "requirement shifting". Using this technique, we also obtain an ETH-tight single-exponential XP algorithm for the Exact Leaf Spanning Tree problem parameterized by clique-width, which settles the final remaining open case for clique-width from the classical Cut and Count of Cygan et al. [FOCS 2011, TALG 2022]. This shows the versatility of our technique and its potential applicability to other problems as well. Additionally, in order to establish our lower and upper bounds we introduce a number of tools which may be of independent interest, including lazy coloring and "asymptotic" SETH-based reductions for structural parameters.
@InProceedings{bojikian_et_al:LIPIcs.ICALP.2026.38,
author = {Bojikian, Narek and Firbas, Alexander and Ganian, Robert and Hoang, Hung P. and Szil\'{a}gyi, Krisztina},
title = {{Fine-Grained Complexity of Computing Degree-Constrained Spanning Trees}},
booktitle = {53rd International Colloquium on Automata, Languages, and Programming (ICALP 2026)},
pages = {38:1--38:14},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-428-4},
ISSN = {1868-8969},
year = {2026},
volume = {374},
editor = {Bhattacharya, Sayan and Nanongkai, Danupon and Benedikt, Michael and Puppis, Gabriele},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2026.38},
URN = {urn:nbn:de:0030-drops-264272},
doi = {10.4230/LIPIcs.ICALP.2026.38},
annote = {Keywords: Parameterized complexity, Structural parameters, Clique-width, fine-grained complexity, Spanning tree}
}