Guarding a 1.5D Terrain with Imprecise Viewpoints
摘要
Given an n-vertex 1.5D terrain \(\mathcal {T}\) and a set of m edges of \(\mathcal {T}\) , we study the problem of placing one viewpoint on each edge so that the total length of the visible portions of the terrain is maximized. We present an \(O(n+m \log ~\hbox {m} )\) time \(\frac{1}{2}\) -approximation algorithm for the general problem, and polynomial-time algorithms for the cases \(m=1\) and \(m=2\) . Additionally, we show that the problem of computing a point on \(\mathcal {T}\) maximizing the visible portion of \(\mathcal {T}\) can be solved in \(O(n^3)\) time.