Linear-Space data structures for range minority query in arrays

  • Authors:
  • Timothy M. Chan;Stephane Durocher;Matthew Skala;Bryan T. Wilkinson

  • Affiliations:
  • Cheriton School of Computer Science, University of Waterloo, Waterloo, Canada;Department of Computer Science, University of Manitoba, Winnipeg, Canada;Department of Computer Science, University of Manitoba, Winnipeg, Canada;Cheriton School of Computer Science, University of Waterloo, Waterloo, Canada

  • Venue:
  • SWAT'12 Proceedings of the 13th Scandinavian conference on Algorithm Theory
  • Year:
  • 2012

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Abstract

We consider range queries in arrays that search for low-frequency elements: least frequent elements and α-minorities. An α-minority of a query range has multiplicity no greater than an α fraction of the elements in the range. Our data structure for the least frequent element range query problem requires O(n) space, O(n3/2) preprocessing time, and $O(\sqrt{n})$ query time. A reduction from boolean matrix multiplication to this problem shows the hardness of simultaneous improvements in both preprocessing time and query time. Our data structure for the α-minority range query problem requires O(n) space, supports queries in O(1/α) time, and allows α to be specified at query time.