Rank-Balanced Trees

  • Authors:
  • Bernhard Haeupler;Siddhartha Sen;Robert E. Tarjan

  • Affiliations:
  • Massachusetts Institute of Technology,;Princeton University,;Princeton University, and HP Laboratories, Palo Alto, 94304

  • Venue:
  • WADS '09 Proceedings of the 11th International Symposium on Algorithms and Data Structures
  • Year:
  • 2009

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Abstract

Since the invention of AVL trees in 1962, a wide variety of ways to balance binary search trees have been proposed. Notable are red-black trees, in which bottom-up rebalancing after an insertion or deletion takes O(1) amortized time and O(1) rotations worst-case. But the design space of balanced trees has not been fully explored. We introduce the rank-balanced tree , a relaxation of AVL trees. Rank-balanced trees can be rebalanced bottom-up after an insertion or deletion in O(1) amortized time and at most two rotations worst-case, in contrast to red-black trees, which need up to three rotations per deletion. Rebalancing can also be done top-down with fixed lookahead in O(1) amortized time. Using a novel analysis that relies on an exponential potential function, we show that both bottom-up and top-down rebalancing modify nodes exponentially infrequently in their heights.