On Selecting Leaves With Disjoint Neighborhoods In Embedded Trees

We present a generalization of a combinatorial result from Aggarwal, Guibas, Saxe and Shor [1] on selecting a fraction of leaves, with pairwise disjoint neighborhoods, in a tree embedded in the plane. This result has been used by linear-time algorithms to compute certain tree-like Voronoi diagrams, such as the Voronoi diagram of points in convex position. Our generalization allows that only a fraction of the tree leaves is considered: Given is a plane tree T of n leaves, m of which have been marked. Each marked leaf is associated with a neighborhood (a subtree of T) and any topologically consecutive marked leaves have disjoint neighborhoods. We show how to select in linear time a constant fraction of the marked leaves that have pairwise disjoint neighborhoods.