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Optimal, output-sensitive algorithms for constructing upper envelope of line segments in parallel
N. Gupta, S. Chopra,
Published in Springer Verlag
Volume: 2245
Pages: 183 - 194
In this paper we focus on the problem of designing very fast parallel algorithms for constructing the upper envelope of straight-line segments that achieve the O(n logH) work-boundfor input size n and output size H. Our algorithms are designed for the arbitrary CRCW PRAM model. We first describe an O(log n ・ (logH + log log n)) time deterministic algorithm for the problem, that achieves O(n logH) work boundfor H = Ω(log n). We present a fast randomized algorithm that runs in expectedtime O(logH ・ log log n) with high probability andd oes O(n logH) work. For logH = Ω(log log n), we can achieve the running time of O(logH) while simultaneously keeping the work optimal. We also present a fast randomized algorithm that runs in ˜O(log n/ log k) time with nk processors, k > logΩ(1) n. The algorithms do not assume any input distribution andthe running times holdwith high probability. © Springer-Verlag Berlin Heidelberg 2001.
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