Computational geometry: an introduction
Computational geometry: an introduction
Minimally covering a horizontally convex orthogonal polygon
SCG '86 Proceedings of the second annual symposium on Computational geometry
Orderings and some combinatorial optimization problems with geometric applications
Orderings and some combinatorial optimization problems with geometric applications
Perfect graphs and orthogonally convex covers
SIAM Journal on Discrete Mathematics
Covering orthogonal polygons with star polygons: the perfect graph approach
Journal of Computer and System Sciences
On covering orthogonal polygons with star-shaped polygons
Information Sciences: an International Journal
Journal of Algorithms
Decomposing a polygon into its convex parts
STOC '79 Proceedings of the eleventh annual ACM symposium on Theory of computing
STOC '84 Proceedings of the sixteenth annual ACM symposium on Theory of computing
The art gallery theorem: its variations, applications and algorithmic aspects
The art gallery theorem: its variations, applications and algorithmic aspects
Polygon decomposition and perfect graphs
Polygon decomposition and perfect graphs
Some NP-hard polygon decomposition problems
IEEE Transactions on Information Theory
Linear-time 3-approximation algorithm for the r-star covering problem
WALCOM'08 Proceedings of the 2nd international conference on Algorithms and computation
Algorithms and theory of computation handbook
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In 1986, Keil provided an O(n2) time algorithm for the problem of covering monotone orthogonal polygons with the minimum number of r-star-shaped orthogonal polygons. This was later improved to O(n) time and space by Gewali et al. in [L. Gewali, M. Keil, S.C. Ntafos, On covering orthogonal polygons with star-shaped polygons, Information Sciences 65 (1992) 45-63]. In this paper we simplify the latter algorithm-we show that with a little modification, the first step Sweep1 of the discussed algorithm-which computes the top ceilings of horizontal grid segments-can be omitted. In addition, for the minimum orthogonal guard problem in the considered class of polygons, our approach provides a linear time algorithm which uses O(k) additional space, where k is the size of the optimal solution-the algorithm in [L. Gewali, M. Keil, S.C. Ntafos, On covering orthogonal polygons with star-shaped polygons, Information Sciences 65 (1992) 45-63] uses both O(n) time and O(n) additional space.