,
Olivier Bodini
,
Francis Durand
,
Bernhard Gittenberger
Creative Commons Attribution 4.0 International license
We present a new exact-size sampler for increasing trees that outputs a tree of size n uniformly at random while avoiding the global coefficient pre-computation required by the classical recursive method of Flajolet et al. [Philippe Flajolet et al., 1994]. The key idea is a hybrid oracle-driven rejection scheme in which local sampling decisions are made using interval bounds on the coefficients, with a fallback to exact recurrence computation only on rare ambiguous events. In the bit-complexity model this yields an expected running time of O(nlog n) and it consumes a number of random bits within O(n) of the Shannon entropy, which is information-theoretically optimal up to lower-order terms. The sampler proceeds in two phases. We first generate the unlabeled rooted ordered shape by recursively sampling node arities and subtree sizes and then draw a uniform permutation of {1,…,n} and apply a deterministic increasing-labeling procedure.
@InProceedings{azzouz_et_al:LIPIcs.AofA.2026.3,
author = {Azzouz, Nadja and Bodini, Olivier and Durand, Francis and Gittenberger, Bernhard},
title = {{Efficient Sampling of Increasing Trees}},
booktitle = {37th International Conference on Probabilistic, Combinatorial and Asymptotic Methods for the Analysis of Algorithms (AofA 2026)},
pages = {3:1--3:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-435-2},
ISSN = {1868-8969},
year = {2026},
volume = {381},
editor = {Panagiotou, Konstantinos},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AofA.2026.3},
URN = {urn:nbn:de:0030-drops-262740},
doi = {10.4230/LIPIcs.AofA.2026.3},
annote = {Keywords: sampling algorithms, bit-complexity, increasing trees, generating functions}
}