Complexity of finding color-avoiding connected components

Source abstract

Two vertices of a (not necessarily properly) arc-colored digraph are called arc-$\ell$-color-avoiding strongly $k$-arc-connected if, after the removal of the arcs of any at most $\ell$ colors, they remain strongly $k$-arc-connected. The arc-$\ell$-color-avoiding strongly $k$-arc-connected components are maximal sets of vertices such that any two of those vertices belonging to the set are arc-$\ell$-color-avoiding strongly $k$-arc-connected in the graph. We investigate the problems of finding the arc-$\ell$-color-avoiding strongly $k$-arc-connected components and the maximal arc-$\ell$-color-avoiding strongly $k$-arc-connected subgraphs of an arc-colored digraph. We also consider possible generalizations to $k$-vertex-connectivity and to vertex-colored digraphs. We show that despite the seemingly minor differences in definitions, the complexity of these problems varies significantly: some can be solved in polynomial time, while others are NP-hard. It also turns out that in some cases the problem is NP-hard when multiple colors can be assigned to each vertex, but the problem becomes polynomial-time solvable when each vertex is single-colored.