Title
Zig-Zag Numberlink is NP-Complete.
Abstract
When can $t$ terminal pairs in an $m \times n$ grid be connected by $t$ vertex-disjoint paths that cover all vertices of the grid? We prove that this problem is NP-complete. Our hardness result can be compared to two previous NP-hardness proofs: Lynch's 1975 proof without the ``cover all vertices'' constraint, and Kotsuma and Takenaga's 2010 proof when the paths are restricted to have the fewest possible corners within their homotopy class. The latter restriction is a common form of the famous Nikoli puzzle \emph{Numberlink}; our problem is another common form of Numberlink, sometimes called \emph{Zig-Zag Numberlink} and popularized by the smartphone app \emph{Flow Free}.
Year
DOI
Venue
2015
10.2197/ipsjjip.23.239
Journal of Information Processing
Keywords
DocType
Volume
np hard,discrete mathematics,games
Journal
23
Issue
Citations 
PageRank 
3
3
0.47
References 
Authors
4
7
Name
Order
Citations
PageRank
Aaron B. Adcock1432.78
Erik D. Demaine24624388.59
Martin L. Demaine359284.37
Michael P. O'Brien430.81
Felix Reidl59912.36
Fernando Sanchez Villaamil6505.97
Blair D. Sullivan710213.93