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On the Complexity of Two Circle Strongly Connecting Problems
September 1992 (vol. 41 no. 9)
pp. 1185-1188

Given n demand points in the plane, the circle strongly connecting problem (CSCP) is to locate n circles in the plane, each with its center in a different demand point, and determine the radius of each circle such that the corresponding digraph G=(V, E), in which a vertex nu /sub 1/ in V stands for the point p/sub i/, and a directed edge ( nu /sub i/, nu /sub j/) in E, if and only if p/sub j/ located within the circle of p/sub i/, is strongly connected, and the sum of the radii of these n circles is minimal. The constrained circle strongly connecting problem is similar to the CSCP except that the points are given in the plane with a set of obstacles and a directed edge ( nu /sub i/, nu /sub j/) in E, if and only if p/sub j/ is located within the circle of p/sub i/ and no obstacles exist between them. It is proven that both these geometric problems are NP-hard. An O(n log n) approximation algorithm that can produce a solution no greater than twice an optimal one is also proposed.

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Index Terms:
complexity; circle strongly connecting problems; demand points; plane; radius; digraph; directed edge; NP-hard; approximation algorithm; computational complexity; computational geometry; directed graphs.
Nen-Fu Huang, "On the Complexity of Two Circle Strongly Connecting Problems," IEEE Transactions on Computers, vol. 41, no. 9, pp. 1185-1188, Sept. 1992, doi:10.1109/12.165400
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