Creative Commons Attribution 3.0 Unported license
Recently, due to the widespread diffusion of smart-phones, mobile puzzle games have experienced a huge increase in their popularity. A successful puzzle has to be both captivating and challenging, and it has been suggested that this features are somehow related to their computational complexity. Indeed, many puzzle games - such as Mah-Jongg, Sokoban, Candy Crush, and 2048, to name a few - are known to be NP-hard. In this paper we consider Trainyard: a popular mobile puzzle game whose goal is to get colored trains from their initial stations to suitable destination stations. We prove that the problem of determining whether there exists a solution to a given Trainyard level is NP. We also provide an implementation of our hardness reduction (see http://trainyard.isnphard.com).
@InProceedings{almanza_et_al:LIPIcs.FUN.2016.2,
author = {Almanza, Matteo and Leucci, Stefano and Panconesi, Alessandro},
title = {{Trainyard is NP-hard}},
booktitle = {8th International Conference on Fun with Algorithms (FUN 2016)},
pages = {2:1--2:14},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-005-7},
ISSN = {1868-8969},
year = {2016},
volume = {49},
editor = {Demaine, Erik D. and Grandoni, Fabrizio},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2016.2},
URN = {urn:nbn:de:0030-drops-58796},
doi = {10.4230/LIPIcs.FUN.2016.2},
annote = {Keywords: Complexity of Games, Trainyard}
}