We consider the on-line problem of representing a sparse bit string by a set of k intervals, where k is much smaller than the length of the string. The goal is to minimize the total length of these intervals under the condition that each 1-bit must be in one of these intervals. We give an efficient greedy algorithm which takes time O(log k) per update (an update involves converting a 0-bit to a 1-bit), which is independent of the size of the entire string. We prove that this greedy algorithm is 2-competitive. We use a natural linear programming relaxation for this problem, and analyze the algorithm by finding a dual feasible solution whose value matches the cost of the greedy algorithm.
@InProceedings{kumar_et_al:LIPIcs.FSTTCS.2012.249, author = {Kumar, Amit and Panda, Preeti R. and Sarangi, Smruti}, title = {{Efficient on-line algorithm for maintaining k-cover of sparse bit-strings}}, booktitle = {IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2012)}, pages = {249--256}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-47-7}, ISSN = {1868-8969}, year = {2012}, volume = {18}, editor = {D'Souza, Deepak and Radhakrishnan, Jaikumar and Telikepalli, Kavitha}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2012.249}, URN = {urn:nbn:de:0030-drops-38639}, doi = {10.4230/LIPIcs.FSTTCS.2012.249}, annote = {Keywords: On-line algorithms, string algorithms} }
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