Weakly Cooperative Guards in Grids
We show that a minimum coverage of a grid of n segments has n–p3 weakly cooperative guards, where p3 is the size of the maximum P3-matching in the intersection graph of the grid. This makes the minimum weakly cooperative guards problem in grids NP-hard, as we prove that the maximum P3-matching problem in subcubic bipartite planar graphs is NP-hard. At last, we propose a 7/6-approximation algorithm for the minimum weakly cooperative guards problem.
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