LIPIcs.CPM.2021.12.pdf
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Computing Covers of 2D-Strings
Authors
Panagiotis Charalampopoulos 
,
Jakub Radoszewski ,
Wojciech Rytter ,
Tomasz Waleń ,
Wiktor Zuba
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Volume:
32nd Annual Symposium on Combinatorial Pattern Matching (CPM 2021)
Series: Leibniz International Proceedings in Informatics (LIPIcs)
Conference: Annual Symposium on Combinatorial Pattern Matching (CPM) - License:
Creative Commons Attribution 4.0 International license
- Publication Date: 2021-06-30
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Panagiotis Charalampopoulos, Jakub Radoszewski, Wojciech Rytter, Tomasz Waleń, and Wiktor Zuba. Computing Covers of 2D-Strings. In 32nd Annual Symposium on Combinatorial Pattern Matching (CPM 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 191, pp. 12:1-12:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)
https://doi.org/10.4230/LIPIcs.CPM.2021.12
Abstract
We consider two notions of covers of a two-dimensional string T. A (rectangular) subarray P of T is a 2D-cover of T if each position of T is in an occurrence of P in T. A one-dimensional string S is a 1D-cover of T if its vertical and horizontal occurrences in T cover all positions of T. We show how to compute the smallest-area 2D-cover of an m × n array T in the optimal 𝒪(N) time, where N = mn, all aperiodic 2D-covers of T in 𝒪(N log N) time, and all 2D-covers of T in N^{4/3}⋅ log^{𝒪(1)}N time. Further, we show how to compute all 1D-covers in the optimal 𝒪(N) time. Along the way, we show that the Klee’s measure of a set of rectangles, each of width and height at least √n, on an n × n grid can be maintained in √n⋅ log^{𝒪(1)}n time per insertion or deletion of a rectangle, a result which could be of independent interest.
Subject Classification
ACM Subject Classification
- Theory of computation → Pattern matching
Keywords
- 2D-string
- cover
- dynamic Klee’s measure problem
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References
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