Simple DFS on the Complement of a Graph and on Partially Complemented Digraphs

Abstract

A complementation operation on a vertex of a digraph changes all outgoing arcs into non-arcs, and outgoing non-arcs into arcs. A partially complemented digraph $\tilde{G}$ is a digraph obtained from a sequence of vertex complement operations on $G$. Dahlhaus et al. showed that, given an adjacency-list representation of $\tilde{G}$, depth-first search (DFS) on $G$ can be performed in $O(n+\tilde{m})$ time, where $n$ is the number of vertices and $\tilde{m}$ is the number of edges in $\tilde{G}$. To achieve this bound, their algorithm makes use of a somewhat complicated stack-like data structure to simulate the recursion stack, instead of implementing it directly as a recursive algorithm. We give a recursive $O(n+\tilde{m})$ algorithm that uses no complicated data-structures.