Lemmings is PSPACE-complete


Lemmings is a computer puzzle game developed by DMA Design and published by Psygnosis in 1991, in which the player has to guide a tribe of lemming creatures to safety through a hazardous landscape, by assigning them specific skills that modify their behavior in different ways. In this paper we study the optimization problem of saving the highest number of lemmings in a given landscape with a given number of available skills. We prove that, if the number of Builder skills is bounded by a polynomial in the size of the landscape, then the maximization problem belongs to NPO. We also show that, with no such restriction, the game is PSPACE-complete, even if there is only one lemming to save. We thereby settle an open problem posed by Cormode in 2004, and again by

DOI: 10.1007/978-3-319-07890-8_29

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@article{Viglietta2014LemmingsIP, title={Lemmings is PSPACE-complete}, author={Giovanni Viglietta}, journal={Theor. Comput. Sci.}, year={2014}, volume={586}, pages={120-134} }