Union-Find with Constant Time Deletions

作者：Alstrup Stephen^*; Thorup Mikkel; Gortz Inge Li; Rauhe Theis; Zwick Uri

来源：ACM Transactions on Algorithms, 2014, 11(1): 6.

DOI：10.1145/2636922

• Union-find
• disjoint sets

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(alpha([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 alpha([M/N]) (n) is a functional inverse of Ackermann%26apos;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(alpha([M/N]) (n)) amortized time. %26lt;br%26gt;Our analysis supplies, in particular, a very concise potential-based amortized analysis of the standard union-find data structure that yields an O(alpha([M/N]) (n)) amortized bound on the cost of find operations. All previous potential-based analyses yielded the weaker amortized bound of O(alpha([M/N]) (N)). Furthermore, our tighter analysis extends to one-path variants of the path compression technique such as path splitting.

• 出版日期2014-10