On the Difficulty of Some Shortest Path Problems

  • Authors:
  • John Hershberger;Subhash Suri;Amit Bhosle

  • Affiliations:
  • -;-;-

  • Venue:
  • STACS '03 Proceedings of the 20th Annual Symposium on Theoretical Aspects of Computer Science
  • Year:
  • 2003

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Abstract

We prove super-linear lower bounds for some shortest path problems in directed graphs, where no such bounds were previously known. The central problem in our study is the replacement paths problem: Given a directed graph G with non-negative edge weights, and a shortest path P = {e1, e2, ..., ep} between two nodes s and t, compute the shortest path distances from s to t in each of the p graphs obtained from G by deleting one of the edges ei. We show that the replacement paths problem requires 驴(m驴n) time in the worst case whenever m = O(n驴n). Our construction also implies a similar lower bound for the k shortest paths problem for a broad class of algorithms that includes all known algorithms for the problem. To put our lower bound in perspective, we note that both these problems (replacement paths and k shortest paths) can be solved in near linear time for undirected graphs.