Given a multiset S of n positive integers and a target integer t, the Subset Sum problem asks to determine whether there exists a subset of S that sums up to t. The current best deterministic algorithm, by Koiliaris and Xu [SODA'17], runs in O~(sqrt{n}t) time, where O~ hides poly-logarithm factors. Bringmann [SODA'17] later gave a randomized O~(n + t) time algorithm using two-stage color-coding. The O~(n+t) running time is believed to be near-optimal. In this paper, we present a simple and elegant randomized algorithm for Subset Sum in O~(n + t) time. Our new algorithm actually solves its counting version modulo prime p>t, by manipulating generating functions using FFT.
@InProceedings{jin_et_al:OASIcs.SOSA.2019.17, author = {Jin, Ce and Wu, Hongxun}, title = {{A Simple Near-Linear Pseudopolynomial Time Randomized Algorithm for Subset Sum}}, booktitle = {2nd Symposium on Simplicity in Algorithms (SOSA 2019)}, pages = {17:1--17:6}, series = {Open Access Series in Informatics (OASIcs)}, ISBN = {978-3-95977-099-6}, ISSN = {2190-6807}, year = {2019}, volume = {69}, editor = {Fineman, Jeremy T. and Mitzenmacher, Michael}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.SOSA.2019.17}, URN = {urn:nbn:de:0030-drops-100436}, doi = {10.4230/OASIcs.SOSA.2019.17}, annote = {Keywords: subset sum, formal power series, FFT} }
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