What is the minimum number of yes-no questions needed to find an m bit number x in the set S = {0,1,…,2m — 1} if up to ℓ answers may be erroneous/false ? In case when the (t + 1)th question is adaptivelyasked after receiving the answer to the tth question, the problem, posed by Ulam and Rényi, is a chapter of Berlekamp's theory of error-correcting communication with feedback. It is known that, with finitely many exceptions, one can find x asking Berlekamp's minimum number qℓ (m) of questions, i.e., the smallest integer q such that 2q ≥ 2m ((q/ℓ) + (q/ℓ-1+ + (q/2) + q + 1). At the opposite, nonadaptive extreme, when all questions are asked in a unique batch before receiving any answer, a search strategy with qℓ(m) questions is the same as an ℓ-error correcting code of length qℓ (m) having 2m codewords. Such codes in general do not exist for ℓ> 1. Focusing attention on the case I = 2, we shall show that, with the exception of m = 2 and m = 4, one can always find an unknown m bit number x ϵ S by asking q2(m) questions in two nonadaptive batches. Thus the results of our paper provide shortest strategies with as little adaptiveness/interaction as possible.
CITATION STYLE
Cicalese, F., & Mundici, D. (1999). Optimal binary search with two unreliable tests and minimum adaptiveness. In Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) (Vol. 1643, pp. 257–266). Springer Verlag. https://doi.org/10.1007/3-540-48481-7_23
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