Journal of Information Processing
Online ISSN : 1882-6652
ISSN-L : 1882-6652
You Should Be Scared of German Ghost
Erik D. DemaineFermi MaMatthew SusskindErik Waingarten
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2015 Volume 23 Issue 3 Pages 293-298


Ghost is a popular word game played by two or more players. Players take turns adding a letter to the end of a growing word fragment, trying not to be the first to complete a valid word. We show that the game, when played on a regular language, is PSPACE-hard, and extend the result to four variants of the game. In addition, we take advantage of a quirk of the German language — that German words can be concatenated together to form longer words — to give a fun extension of our proof of PSPACE-hardness to subsets of the German language.

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© 2015 by the Information Processing Society of Japan
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