Performance of height-balanced trees

Abstract

This paper presents the results of simulations that investigate the performance of height-balanced (HB[k]) trees. It is shown that the only statistic of HB[1] trees (AVL trees) that is a function of the size of the tree is the time to search for an item in the tree. For sufficiently large trees, the execution times of all procedures for maintaining HB[1] trees are independent of the size of the tree. In particular, an average of .465 restructures are required per insertion, with an average of 2.78 nodes revisited to restore the HB[1] property; an average of .214 restructures are required per deletion, with an average of 1.91 nodes revisited to restore the HB[1] property. Moreover, the execution times of procedures for maintaining HB[k] trees, for k > 1, are also independent of the size of the tree except for the average number of nodes revisited on a delete operation in order to restore the HB[k] property on traceback. The cost of maintaining HB[k] trees drops sharply as the allowable imbalance (k) increases. Both analytical and experimental results that show the cost of maintaining HB[k] trees as a function of k are discussed.