Asymmetric R\'enyi Problem and PATRICIA Tries

TL;DR

This paper investigates an asymmetric variant of Re9nyi's problem, analyzing the number of queries needed for complete or partial recovery of labelings, revealing phase transitions and new asymptotic behaviors, with applications to PATRICIA tries.

Contribution

It introduces a unified approach to analyze the asymmetric Re9nyi problem, deriving precise asymptotics and phase transition phenomena, and extends findings to PATRICIA tries.

Findings

Depth D_n converges in probability but not almost surely.

Height H_n and fillup level F_n exhibit phase transitions at certain p values.

External profile analysis yields new asymptotic results and insights.

Abstract

In 1960, R\'enyi asked for the number of random queries necessary to recover a hidden bijective labeling of n distinct objects. In each query one selects a random subset of labels and asks, what is the set of objects that have these labels? We consider here an asymmetric version of the problem in which in every query an object is chosen with probability p > 1/2 and we ignore "inconclusive" queries. We study the number of queries needed to recover the labeling in its entirety (the height), to recover at least one single element (the fillup level), and to recover a randomly chosen element (the typical depth). This problem exhibits several remarkable behaviors: the depth D_n converges in probability but not almost surely and while it satisfies the central limit theorem its local limit theorem doesn't hold; the height H_n and the fillup level F_n exhibit phase transitions with respect to p in the second term. To obtain these results, we take a unified approach via the analysis of the external profile, defined at level k as the number of elements recovered by the kth query. We first establish new precise asymptotic results for the average and variance, and a central limit law, for the external profile in the regime where it grows polynomially with n. We then extend the external profile results to the boundaries of the central region, leading to the solution of our problem for the height and fillup level. As a bonus, our analysis implies novel results for analogous parameters of random PATRICIA tries.