Enumerating Permutations Sortable by k Passes Through a Pop-Stack
Séminaire lotharingien de combinatoire, 80B (2018)
In an exercise in the first volume of his famous series of books, Knuth considered sorting permutations by passing them through a stack. Many variations of this exercise have since been considered, including allowing multiple passes through the stack and using different data structures. We are concerned with a variation using pop-stacks that was introduced by Avis and Newborn in 1981. Let Pk(x) be the generating function for the permutations sortable by k passes through a pop-stack. The generating function P2(x) was recently given by Pudwell and Smith (the case k=1 being trivial). We show that Pk(x) is rational for any k. Moreover, we give an algorithm to derive Pk(x), and using it we determine the generating functions Pk(x) for k = 6.
@article{SLC_2018_80B_a42,
author = {Anders Claesson and Bjarki \'Ag\'ust Gu{\dh}mundsson},
title = {Enumerating {Permutations} {Sortable} by k {Passes} {Through} a {Pop-Stack}},
journal = {S\'eminaire lotharingien de combinatoire},
year = {2018},
volume = {80B},
url = {http://geodesic.mathdoc.fr/item/SLC_2018_80B_a42/}
}
Anders Claesson; Bjarki Ágúst Guðmundsson. Enumerating Permutations Sortable by k Passes Through a Pop-Stack. Séminaire lotharingien de combinatoire, 80B (2018). http://geodesic.mathdoc.fr/item/SLC_2018_80B_a42/