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Checking Mergeable Priority Queues
 In Digest of the 24th Symposium on FaultTolerant Computing
, 1994
"... We present an efficient algorithm which can check the answers given by the fundamental abstract data types priority queues and mergeable priority queues. This is the first lineartime checker for mergeable priority queues. These abstract data types are widely used in routing, scheduling, simulation, ..."
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We present an efficient algorithm which can check the answers given by the fundamental abstract data types priority queues and mergeable priority queues. This is the first lineartime checker for mergeable priority queues. These abstract data types are widely used in routing, scheduling, simulation, computational geometry and many other algorithmic domains. We have implemented our answer checker and have performed experiments comparing the speed of our checker to recently benchmarked priority queue and mergeable priority queue implementations, and our checker is substantially faster than the best of these implementations. 1 Introduction This paper concerns the fundamental abstract data types of priority queues (PQs) and mergeable priority queues (MPQs). These abstract data types have been recognized as centrally important from the early days of computeralgorithm design. They appear in seminal algorithm texts such as Knuth's [10] and Aho, Hopcroft and Ullman's [1]. Data structure impl...
Upper and Lower Bounds on Constructing Alphabetic Binary Trees
 Proceedings of the 4 th ACMSIAM Symposium on Discrete Algorithms
, 1993
"... This paper studies the longstanding open question of whether optimal alphabetic binary trees can be constructed in o(n lg n) time. We show that a class of techniques for finding optimal alphabetic trees which includes all current methods yielding O(n lg n) time algorithms are at least as hard as so ..."
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Cited by 7 (0 self)
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This paper studies the longstanding open question of whether optimal alphabetic binary trees can be constructed in o(n lg n) time. We show that a class of techniques for finding optimal alphabetic trees which includes all current methods yielding O(n lg n) time algorithms are at least as hard as sorting in whatever model of computation is used. We also give O(n) time algorithms for the case where all the input weights are within a constant factor of one another and when they are exponentially separated. 1 Overview The problem of finding optimal alphabetic binary trees can be stated as follows: Given a sequence of n positive weights w 1 ; : : : ; wn , construct a binary tree whose leaves have these weights, such that the tree is optimal with respect to some cost function and also has the property that the weights on the leaves occur in order as the tree is traversed from left to right. A tree which satisfies this last requirement is said to be alphabetic. Although more general cost fu...
Optimum Alphabetic Binary Trees
 in Combinatorics and Computer Science, ser. Lecture Notes in Computer Science
, 1996
"... We describe a modification of the HuTucker algorithm for constructing an optimal alphabetic tree that runs in O(n) time for several classes of inputs. These classes can be described in simple terms and can be detected in linear time. We also give simple conditions and a linear algorithm for determ ..."
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We describe a modification of the HuTucker algorithm for constructing an optimal alphabetic tree that runs in O(n) time for several classes of inputs. These classes can be described in simple terms and can be detected in linear time. We also give simple conditions and a linear algorithm for determining, in some cases, if two adjacent nodes will be combined in the optimal alphabetic tree.
Checking and Certifying Computational Results
, 1994
"... For many years, there has been tremendous interest in methods to make computation more reliable. In this thesis, we explore various techniques that can be implemented in software to help insure the correctness of the output of a program. The basic tool we use is a generalization of the notion of a p ..."
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For many years, there has been tremendous interest in methods to make computation more reliable. In this thesis, we explore various techniques that can be implemented in software to help insure the correctness of the output of a program. The basic tool we use is a generalization of the notion of a program checker called a certifier. A certifier is given intermediate computations from a program computing an answer in an effort to simplify the checking process. The certifier is constructed in such a way that even if the intermediate computations it is given are incorrect, the certifier will never accept an incorrect output. We have constructed certifiers and program checkers for several common abstract data types including mergeable priority queues and splittable priority queues. We have also constructed a certifier for an abstract data type that allows approximate nearest neighbor queries to be performed efficiently. We have implemented and experimentally evaluated some of these algorithms. In the parallel domain, we have developed both general and problem specific techniques for certifying parallel computation. Lastly, we have formally proven correct a certifier for sorting, and have analyzed the advantages of using certifiers in conjunction with formal program verification techniques. This work forms a thesis presented by Jonathan D. Bright to the faculty of the Department of Computer Science, at the Johns Hopkins University, in partial fulfillment of the requirements for the degree of Doctor of Philosophy, under the supervision of Professor Gregory F. Sullivan. iii Acknowledgements I would like to thank my advisor, Gregory Sullivan, for giving me an excellent research topic for my thesis, and for vastly improving my writing skills during my stay at Hopkins. Also, ...
BlackBox Correctness Tests for Basic Parallel Data Structures ∗
"... Abstract. Operations on basic data structures such as queues, priority queues, stacks, and counters can dominate the execution time of a parallel program due to both their frequency and their coordination and contention overheads. There are considerable performance payoffs in developing highly optim ..."
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Abstract. Operations on basic data structures such as queues, priority queues, stacks, and counters can dominate the execution time of a parallel program due to both their frequency and their coordination and contention overheads. There are considerable performance payoffs in developing highly optimized, asynchronous, distributed, cacheconscious, parallel implementations of such data structures. Such implementations may employ a variety of tricks to reduce latencies and avoid serial bottlenecks, as long as the semantics of the data structure are preserved. The complexity of the implementation and the difficulty in reasoning about asynchronous systems increases concerns regarding possible bugs in the implementation. In this paper we consider postmortem, blackbox procedures for testing whether a parallel data structure behaved correctly. We present the first systematic study of algorithms and hardness results for such testing procedures, focusing on queues, priority queues, stacks, and counters, under various important scenarios. Our results demonstrate the importance of selecting test data such that distinct values are inserted into the data structure (as appropriate). In such cases we present an O(n) time algorithm for testing linearizable queues, an O(n log n) time algorithm for testing linearizable priority queues, and an O(np2) time algorithm for testing sequentially consistent queues, where n is the number of data structure operations and p is the