English

The parity search problem

Combinatorics 2016-03-22 v1

Abstract

We prove that for any positive integers nn and dd there exists a collection consisting of f=dlogn+O(1)f=d\log n+O(1) subsets A1,A2,,AfA_1, A_2, \ldots, A_f of [n][n] such that for any two distinct subsets XX and YY of [n][n] whose size is at most dd there is an index i[f]i\in [f] for which AiX| A_i\cap X| and AiY|A_i\cap Y| have different parity. Here we think of dd as fixed whereas nn is thought of as tending to infinity, and the base of the logarithm is 22. Translated into the language of combinatorial search theory, this tells us that dlogn+O(1) d \log n+O(1) queries suffice to identify up to dd marked items from a totality of nn items if the answers one gets are just whether an even or an odd number of marked elements has been queried, even if the search is performed non-adaptively. Since the entropy method easily yields a matching lower bound for the adaptive version of this problem, our result is asymptotically best possible. This answers a question posed by D\'aniel Gerbner and Bal\'azs Patk\'os in Gyula O.H. Katona's Search Theory Seminar at the R\'enyi institute.

Keywords

Cite

@article{arxiv.1603.06164,
  title  = {The parity search problem},
  author = {Christian Reiher},
  journal= {arXiv preprint arXiv:1603.06164},
  year   = {2016}
}
R2 v1 2026-06-22T13:14:37.855Z