On the enumeration of permutation-invariant and complete Naples parking functions

TL;DR

This paper develops a combinatorial approach to enumerate permutation-invariant and complete Naples parking functions, providing formulas and recursive methods for their counting, building on previous characterizations and simplifying existing descriptions.

Contribution

It introduces an effective enumeration method for permutation-invariant and complete Naples parking functions using combinatorial decompositions, advancing understanding of their structure.

Findings

Derived recursive formulas for counting Naples parking functions

Provided combinatorial decompositions simplifying enumeration

Connected new enumeration methods with previous characterizations

Abstract

Naples parking functions were introduced as a generalization of classical parking functions, in which cars are allowed to park backwards, by checking up to a fixed number of previous slots, before proceedings forward as usual. In our previous work (arXiv:2405.07522, 2024) we have provided a characterization of Naples parking functions in terms of the new notion of \emph{complete parking preference}. Our result also allowed us to describe a new characterization of permutation-invariant Naples parking functions, equivalent (but much simpler) to the one given by Carvalho et al.(arXiv:2109.01735, 2021) but using a completely different approach (and language). In the present article we address some natural enumerative issues concerning the above mentioned objects. We propose an effective approach to enumerate permutation-invariant Naples parking functions and complete Naples parking functions which is based on some natural combinatorial decompositions. We thus obtain formulas depending on some (generally simpler) quantities, which are of interest in their own right, and that can be described in a recursive fashion.