Finding longest increasing and common subsequences in streaming data

David Liben-Nowell (), Erik Vee () and An Zhu ()
Additional contact information
David Liben-Nowell: Carleton College
Erik Vee: IBM, Almaden Research Center
An Zhu: Google, Inc.

Journal of Combinatorial Optimization, 2006, vol. 11, issue 2, No 4, 155-175

Abstract: Abstract We present algorithms and lower bounds for the Longest Increasing Subsequence (LIS) and Longest Common Subsequence (LCS) problems in the data-streaming model. To decide if the LIS of a given stream of elements drawn from an alphabet αbet has length at least k, we discuss a one-pass algorithm using O(k log αbetsize) space, with update time either O(log k) or O(log log αbetsize); for αbetsize = O(1), we can achieve O(log k) space and constant-time updates. We also prove a lower bound of Ω(k) on the space requirement for this problem for general alphabets αbet, even when the input stream is a permutation of αbet. For finding the actual LIS, we give a ⌈log (1 + 1/ɛ)-pass algorithm using O(k1+ɛlog αbetsize) space, for any ɛ > 0. For LCS, there is a trivial Θ(1)-approximate O(log n)-space streaming algorithm when αbetsize = O(1). For general alphabets αbet, the problem is much harder. We prove several lower bounds on the LCS problem, of which the strongest is the following: it is necessary to use Ω(n/ρ2) space to approximate the LCS of two n-element streams to within a factor of ρ, even if the streams are permutations of each other.

Keywords: LIS; LCS; Data-streaming model; Algorithms; Lower bounds (search for similar items in EconPapers)
Date: 2006
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DOI: 10.1007/s10878-006-7125-x

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