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k-Restricted Rotation with an Application to Search Tree Rebalancing

Luccio, Fabrizio and Mesa Enriquez, Antonio and Pagli, Linda (2005) k-Restricted Rotation with an Application to Search Tree Rebalancing. Technical Report del Dipartimento di Informatica . Università di Pisa, Pisa, IT.

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    The restricted rotation distance d_{R}(S,T) between two binary trees S, T of n vertices is the minimum number of rotations by which S can be transformed into T, where rotations can only take place at the root of the tree, or at the right child of the root. A sharp upper bound d_{R}(S,T) \leq 4n-8 is known, based on the word metric of Thompson's group. We refine this bound to a sharp d_{R}(S,T) \leq 4n-8-\rho_{S}-\rho_{T}, where \rho_{S} and \rho_{T} are the numbers of vertices in the rightmost vertex chains of the two trees, by means of a very simple transformation algorithm based on elementary properties of trees. We then generalize the concept of restricted rotation to k-restricted rotation, by allowing rotations to take place at all the vertices of the highest k levels of the tree. For k=2 we show that not much is gained in the worst case, although the classical problem of rebalancing an AVL tree can be solved efficiently, in particular rebalancing after vertex deletion requires O(log n) rotations as in the standard algorithm. Finding significant bounds and applications for k \geq 3 is open.

    Item Type: Book
    Uncontrolled Keywords: Rotation, Rotation distance, Binary tree, Search tree, AVL tree, Rebalancing, Data structures, Design of algorithms.
    Subjects: Area01 - Scienze matematiche e informatiche > INF/01 - Informatica
    Divisions: Dipartimenti (until 2012) > DIPARTIMENTO DI INFORMATICA
    Depositing User: dott.ssa Sandra Faita
    Date Deposited: 09 Dec 2014 11:18
    Last Modified: 09 Dec 2014 11:18
    URI: http://eprints.adm.unipi.it/id/eprint/2132

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