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Cascade Heap: Towards Time-Optimal Extractions
Heaps are well-studied fundamental data structures, having myriads of applications, both theoretical and practical. We consider the problem of designing a heap with an “optimal” extract-min operation. Assuming an arbitrary linear ordering of keys, a heap with n elements typically takes O(log n) time to extract the minimum. Extracting all elements faster is impossible as this would violate the Ω (nlog n) bound for comparison-based sorting. It is known, however, that is takes only O(n+ klog k) time to sort just k smallest elements out of n given, which prompts that there might be a faster heap, whose extract-min performance depends on the number of elements extracted so far. In this paper we show that this is indeed the case. We present a version of heap that performs insert in O(1) time and takes only O(log ∗ n+ log k) time to carry out the k-th extraction (where log ∗ denotes the iterated logarithm). All the above bounds are worst-case. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.