On the complexity of time-dependent shortest paths

  • Authors:
  • Luca Foschini;John Hershberger;Subhash Suri

  • Affiliations:
  • University of California, Santa Barbara, CA;Mentor Graphics Corp, Wilsonville, OR;University of California, Santa Barbara, CA

  • Venue:
  • Proceedings of the twenty-second annual ACM-SIAM symposium on Discrete Algorithms
  • Year:
  • 2011

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Abstract

We investigate the complexity of shortest paths in time-dependent graphs, in which the costs of edges vary as a function of time, and as a result the shortest path between two nodes s and d can change over time. Our main result is that when the edge cost functions are (polynomial-size) piecewise linear, the shortest path from s to d can change nθ(log n) times, settling a several-year-old conjecture of Dean [Technical Reports, 1999, 2004]. We also show that the complexity is polynomial if the slopes of the linear function come from a restricted class, present an output-sensitive algorithm for the general case, and describe a scheme for a (1 + ε)-approximation of the travel time function in near-quadratic space. Finally, despite the fact that the arrival time function may have superpolynomial complexity, we show that a minimum delay path for any departure time interval can be computed in polynomial time.