Work-Time Optimal k-Merge Algorithms on the PRAM

  • Authors:
  • Tatsuya Hayashi;Koji Nakano;Stephan Olariu

  • Affiliations:
  • -;-;-

  • Venue:
  • IEEE Transactions on Parallel and Distributed Systems
  • Year:
  • 1998

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Abstract

For 2 驴k驴n, the k-merge problem is to merge a collection of k sorted sequences of total length n into a new sorted sequence. The k-merge problem is fundamental as it provides a common generalization of both merging and sorting. The main contribution of this work is to give simple and intuitive work-time optimal algorithms for the k-merge problem on three PRAM models, thus settling the status of the k-merge problem. We first prove that 驴(n log k) work is required to solve the k-merge problem on the PRAM models. We then show that the EREW-PRAM and both the CREW-PRAM and the CRCW require 驴(log n) time and 驴(log log n + log k) time, respectively, provided that the amount of work is bounded by O(n log k). Our first k-merge algorithm runs in 驴(log n) time and performs 驴(n log k) work on the EREW-PRAM. Finally, we design a work-time optimal CREW-PRAM k-merge algorithm that runs in 驴(log log n + log k) time and performs 驴(n log k) work. This latter algorithm is also work-time optimal on the CRCW-PRAM model. Our algorithms completely settle the status of the k-merge problem on the three main PRAM models.