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arXiv 1302.6641cs.DS
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为什么有些堆支持常数摊销时间减少键操作,而有些堆不支持

Why some heaps support constant-amortized-time decrease-key operations, and others do not

John Iacono

摘要:

一个下界表明,一类堆算法的指针模型中,只有堆指针必须花费欧米茄(日志n /日志n)摊销时间上的减少键操作(给定O(日志n)摊销时间提取分钟)。直观地说,这个界限显示了O(1)-time decrease的关键-关键是在O(log n)时间内排序O(log n)项的能力; Fibonacci堆[M. L. Fredman和R. E.塔扬J. ACM 34(3):596-615(1987)]通过使用桶排序来实现这一点。我们的下限也保持无论有多少数据被增强;这是相对于Fredman的下限[J. ACM 46(4):473-501(1999)],其显示了增强位的数量和decrease-key的摊销成本之间的权衡。提出了一种新的堆数据结构--排序堆。这个堆是Elmasry堆的简化[SODA 2009:471-476],并与它共享一个O(log log n)摊销时间减少键,但有一个简单的实现,这样我们的下限就成立了。因此,一个自然的模型,提出了一个基于指针的堆,使摊销的运行时间的自调整结构和摊销的下降键的渐近下界不同,但O(日志n)的因素。

英文摘要:

A lower bound is presented which shows that a class of heap algorithms in the pointer model with only heap pointers must spend Omega(log log n / log log log n) amortized time on the decrease-key operation (given O(log n) amortized-time extract-min). Intuitively, this bound shows the key to having O(1)-time decrease-key is the ability to sort O(log n) items in O(log n) time; Fibonacci heaps [M.L. Fredman and R. E. Tarjan. J. ACM 34(3):596-615 (1987)] do this through the use of bucket sort. Our lower bound also holds no matter how much data is augmented; this is in contrast to the lower bound of Fredman [J. ACM 46(4):473-501 (1999)] who showed a tradeoff between the number of augmented bits and the amortized cost of decrease-key. A new heap data structure, the sort heap, is presented. This heap is a simplification of the heap of Elmasry [SODA 2009: 471-476] and shares with it a O(log log n) amortized-time decrease-key, but with a straightforward implementation such that our lower bound holds. Thus a natural model is presented for a pointer-based heap such that the amortized runtime of a self-adjusting structure and amortized lower asymptotic bounds for decrease-key differ by but a O(log log log n) factor.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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