Pancake Flipping is Hard

Laurent Bulteau (1) , Guillaume Fertin (1) , Irena Rusu (1)

1 LINA - Laboratoire d'Informatique de Nantes Atlantique

Pancake Flipping is the problem of sorting a stack of pancakes of different sizes (that is, a permutation), when the only allowed operation is to insert a spatula anywhere in the stack and to flip the pancakes above it (that is, to perform a prefix reversal). In the burnt variant, one side of each pancake is marked as burnt, and it is required to finish with all pancakes having the burnt side down. Computing the optimal scenario for any stack of pancakes and determining the worst-case stack for any stack size have been challenges over more than three decades. Beyond being an intriguing combinatorial problem in itself, it also yields applications, e.g. in parallel computing and computational biology. In this paper, we show that the Pancake Flipping problem, in its original (unburnt) variant, is NP-hard, thus answering the long-standing question of its computational complexity.

Domaines: Complexité [cs.CC]; Bio-informatique [q-bio.QM]; Bio-Informatique, Biologie Systémique [q-bio.QM]

Laurent Bulteau, Guillaume Fertin, Irena Rusu. Pancake Flipping is Hard. 37th International Symposium on Mathematical Foundations of Computer Science (MFCS 2012), Aug 2012, Bratislava, Slovakia. pp.247-258. ⟨hal-00717712⟩