Labeled shortest paths in digraphs with negative and positive edge weights

¹ Department of Computer Science, The University of Alabama, Box 870290, Tuscaloosa, AL 35487-0290, USA; pgb@cs.ua.edu
² Mercer University, Department of Computer Science, 1400 Coleman Ave, Macon, GA 31207, USA; David.A.Thomas@student.Mercer.edu

Received: 5 October 2006
Accepted: 6 January 2009

Abstract

This paper gives a shortest path algorithm for CFG (context free grammar) labeled and weighted digraphs where edge weights may be positive or negative, but negative-weight cycles are not allowed in the underlying unlabeled graph. These results build directly on an algorithm of Barrett et al. [SIAM J. Comput. 30 (2000) 809–837]. In addition to many other results, they gave a shortest path algorithm for CFG labeled and weighted digraphs where all edges are nonnegative. Our algorithm is based closely on Barrett et al.'s algorithm as well as Johnson's algorithm for shortest paths in digraphs whose edges may have positive or negative weights.