Optimum lopsided binary trees

  • Authors:
  • Sanjiv Kapoor;Edward M. Reingold

  • Affiliations:
  • Indian Institute of Technology, New Delhi, India;Univ. of Illinois at Urbana-Champaign, Urbana

  • Venue:
  • Journal of the ACM (JACM)
  • Year:
  • 1989

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Abstract

Binary search trees with costs &agr; and &bgr;, respectively, on the left and right edges (lopsided search trees) are considered. The exact shape, minimum worst-case cost, and minimum average cost of lopsided trees of n internal nodes are determined for nonnegative &agr; and &bgr;; the costs are both roughly logp(n + 1) where p is the unique real number in the interval (1. 2] satisfying 1/p&agr; + 1/p&bgr; = 1. Search procedures are given that come within a small additive constant of the lower bounds. Almost-optimum algorithms for the lopsided case of unbounded searching are also obtained. Some extensions to nonconstant costs are briefly sketched.