Given a sequence of elements, we consider the problem of indexing the sequence to support range mode queries - given a query range, find the element with maximum frequency in the range. We give indexing data structures for this problem; given a sequence, we construct a data structure that can be used later to process arbitrary queries. Our algorithms are efficient for small maximum frequency cases. We also consider a natural generalization of the problem: the range mode enumeration problem, for which there has been no known efficient algorithms. Our algorithms have query time complexities which are linear in the output size plus small terms.
@InProceedings{sumigawa_et_al:LIPIcs.ISAAC.2020.29, author = {Sumigawa, Kentaro and Chakraborty, Sankardeep and Sadakane, Kunihiko and Satti, Srinivasa Rao}, title = {{Enumerating Range Modes}}, booktitle = {31st International Symposium on Algorithms and Computation (ISAAC 2020)}, pages = {29:1--29:16}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-173-3}, ISSN = {1868-8969}, year = {2020}, volume = {181}, editor = {Cao, Yixin and Cheng, Siu-Wing and Li, Minming}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ISAAC.2020.29}, URN = {urn:nbn:de:0030-drops-133732}, doi = {10.4230/LIPIcs.ISAAC.2020.29}, annote = {Keywords: range mode, space-efficient data structure, enumeration algorithm} }
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