Selection from read-only memory and sorting with minimum data movement

  • Authors:
  • J. Ian Munro;Venkatesh Raman

  • Affiliations:
  • Univ. of Waterloo, Waterloo, Ont., Canada;Institute of Mathematical Sciences, Madras, India

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 1996

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Abstract

Selecting an element of given rank, for example the median, is afundamental problem in data organization and the computationalcomplexity of comparison based problems. Here, we consider the scenarioin which the data resides in an array of read-only memory and hence theelements cannot be moved within the array. Under this model, we developefficient selection algorithms using very little extra space(ologn extra storage cells). These include anOn1+3 worst case algorithm and an Onloglogn average case algorithm, both using a constant numberof extra storage cells or indices. Our algorithms complement the upperbounds for the time-space tradeoffs obtained by Munro and Paterson [9]and Frederickson [4] who developed algorithms for selection in the samemodel when Wlogn2 extra storage cells are available.We apply our selection algorithms to obtain sorting algorithms thatperform the minimum number of data moves on any given array. We alsoderive upper bounds for time-space tradeoffs for sorting with minimumdata movement.—Authors' Abstract