On Fair Covering and Hitting Problems

In this paper, we study two generalizations of Vertex Cover and Edge Cover, namely Colorful Vertex Cover and Colorful Edge Cover. In the Colorful Vertex Cover problem, given an n-vertex edge-colored graph G with colors from { 1, …, ω} and coverage requirements r₁, r₂, …, r_ω, the goal is to find a minimum-sized set of vertices that are incident on at least r_i edges of color i, for each 1 ≤ i≤ ω, i.e., we need to cover at least r_i edges of color i. Colorful Edge Cover is similar to Colorful Vertex Cover except here we are given a vertex-colored graph and the goal is to cover at least r_i vertices of color i, for each 1 ≤ i≤ ω, by a minimum-sized set of edges. These problems have several applications in fair covering and hitting of geometric set systems involving points and lines that are divided into multiple groups. Here, “fairness” ensures that the coverage (resp. hitting) requirement of every group is fully satisfied. We obtain a (2 + ϵ) -approximation for the Colorful Vertex Cover problem in time n^{O ( ω / ϵ )}, i.e., we obtain an O(1)-approximation in polynomial time for constant number of colors. Next, for the Colorful Edge Cover problem, we design an O(ωn³) time exact algorithm, via a chain of reductions to a matching problem. For all intermediate problems in this chain of reductions, we design polynomial time algorithms, which might be of independent interest.