Multiple-Size Divide-and-Conquer Recurrences* Ming-Yang Kao t Department of Computer Science Duke University Durham, N C 27708 U.S.A. kao~cs.duke.edu Introduction This note reports a tight asymptotic solution to the following recurrence on all positive integers n: T(n) = c-n - log o n + E,~I ai.T(Fbi-n]) for n _> no, 0 < T(n) < d for n < no, where ¢ (1) (2) ~ >_ 0,/~_> 0, c > 0, d > 0, ¢ k is a positive integer, ¢ ai>0andl>bi>0fori=l,...,k, ¢ no ~> marx,_- 1 --- /r 1 1--bi " Since no _> max,= 1 1---~,1 Fbi.nl < n - 1 for all b~ and n >_ no. Thus, the T(n) term on the left-hand side of (1) is defined on T-terms with smaller n, and (2) properly specifies the initial values of T. A special case of this recurrence, namely, k = 1, is discussed in [2, 5] and standard textbooks on algorithms and is used extensively to analyze divide-and-conquer strategies [1, 4]. A specific recurrence with k - 2 is used to analyze a divide-and-conquer algorithm for selecting a key with a given rank [1, 3, 4]. *A version of this work appeared in Proceedings of
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