Paper Info
Title
Union-Find with Constant Time Deletions
Abstract
A union-find data structure maintains a collection of disjoint sets under the operations makeset, union, and find. Kaplan, Shafrir, and Tarjan [SODA 2002] designed data structures for an extension of the union-find problem in which items of the sets maintained may be deleted. The cost of a delete operation in their implementations is essentially the same as the cost of a find operation; namely, O(log n) worst-case and O(α⌈ M/N⌉ (n)) amortized, where n is the number of items in the set returned by the find operation, N is the total number of makeset operations performed, M is the total number of find operations performed, and α⌈ M/N⌉(n) is a functional inverse of Ackermann’s function. They left open the question whether delete operations can be implemented more efficiently than find operations, for example, in o(log n) worst-case time. We resolve this open problem by presenting a relatively simple modification of the classical union-find data structure that supports delete, as well as makeset and union operations, in constant worst-case time, while still supporting find operations in O(log n) worst-case time and O(α⌈ M/N⌉ (n)) amortized time. Our analysis supplies, in particular, a very concise potential-based amortized analysis of the standard union-find data structure that yields an O(α⌈ M/N⌉ (n)) amortized bound on the cost of find operations. All previous potential-based analyses yielded the weaker amortized bound of O(α⌈ M/N⌉ (N)). Furthermore, our tighter analysis extends to one-path variants of the path compression technique such as path splitting.
Year
DOI
Venue
2005
10.1145/2636922
ACM Transactions on Algorithms
Keywords
DocType
Volume
data structure
Conference
11
Issue
ISSN
ISBN
1
1549-6325
3-540-27580-0
Citations 
PageRank 
References 
4
0.42
20
Authors
6
Name
Order
Citations
PageRank
Stephen Alstrup165742.60
Inge Li Gørtz212820.94
Theis Rauhe366135.11
Mikkel Thorup45081366.30
Uri Zwick53586257.02
IL Gortz6110.95