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Given a rooted binary tree T and a tuple (w, h), we wish to test whether there exists a strict upward drawing of T on a w × h grid; that is, a planar grid drawing with straight-line edges where every vertex has a strictly lower y-coordinate than its parent. [Biedl and Mondal, 2017] prove that this problem is NP-hard for general trees; their construction crucially uses nodes of very high degree. [Akatiya et al., 2018] prove that the problem is also NP-hard for binary trees with a fixed combinatorial embedding; their construction crucially relies on the fixed embedding. Both pose the question for binary trees and a free embedding as an open problem. Here, we show that this problem is also NP-hard.
@InProceedings{loffler:LIPIcs.GD.2024.47,
author = {L\"{o}ffler, Maarten},
title = {{Strict Upward Planar Grid Drawings of Binary Trees with Minimal Area}},
booktitle = {32nd International Symposium on Graph Drawing and Network Visualization (GD 2024)},
pages = {47:1--47:3},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-343-0},
ISSN = {1868-8969},
year = {2024},
volume = {320},
editor = {Felsner, Stefan and Klein, Karsten},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.GD.2024.47},
URN = {urn:nbn:de:0030-drops-213311},
doi = {10.4230/LIPIcs.GD.2024.47},
annote = {Keywords: Upward drawings, grid drawings, minimal area}
}