Suppose a language L can be decided by a bounded-error randomized algorithm that runs in space S and time n * poly(S). We give a randomized algorithm for L that still runs in space O(S) and time n * poly(S) that uses only O(S) random bits; our algorithm has a low failure probability on all but a negligible fraction of inputs of each length. As an immediate corollary, there is a deterministic algorithm for L that runs in space O(S) and succeeds on all but a negligible fraction of inputs of each length. We also give several other complexity-theoretic applications of our technique.
@InProceedings{hoza:LIPIcs.CCC.2019.9, author = {Hoza, William M.}, title = {{Typically-Correct Derandomization for Small Time and Space}}, booktitle = {34th Computational Complexity Conference (CCC 2019)}, pages = {9:1--9:39}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-116-0}, ISSN = {1868-8969}, year = {2019}, volume = {137}, editor = {Shpilka, Amir}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CCC.2019.9}, URN = {urn:nbn:de:0030-drops-108317}, doi = {10.4230/LIPIcs.CCC.2019.9}, annote = {Keywords: Derandomization, pseudorandomness, space complexity} }
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