Efficient Reorganization of Binary Search Trees

We consider the problem of maintaining a binary search tree (BST) that minimizes the average access cost needed to satisfy randomly generated requests. We analyze scenarios in which the accesses are generated according to a vector of fixed probabilities which is unknown. Our approach is statistical. We devise policies for modifying the tree structure dynamically, using rotations of accessed records. The aim is to produce good approximations of the optimal structure of the tree, while keeping the number of rotations as small as possible. The heuristics that we propose achieve a close approximation to the optimal BST, with lower organization costs than any previously studied. We introduce the MOVE ONCE rule. The average access cost to the tree under this rule is shown to equal the value achieved by the common rule Move to the Root (MTR). The advantage of MOVE ONCE over MTR and similar rules is that it relocates each of the items in the tree at most once. We show that the total expected ...

• Type: Conference
• Year: 1994
• Where: CIAC
• Authors: Micha Hofri, Hadas Shachnai
• Keywords: Algorithms, Average Access Cost, Binary Search Tree, CIAC 1994, MOVE ONCE Rule