Trade-offs for fully dynamic transitive closure on DAGs: breaking through the O(n2 barrier

  • Authors:
  • Camil Demetrescu;Giuseppe F. Italiano

  • Affiliations:
  • Università di Roma “La Sapienza”, Rome, Italy;Università di Roma “Tor Vergata”, Rome, Italy

  • Venue:
  • Journal of the ACM (JACM)
  • Year:
  • 2005

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Abstract

We present an algorithm for directed acyclic graphs that breaks through the O(n2) barrier on the single-operation complexity of fully dynamic transitive closure, where n is the number of edges in the graph. We can answer queries in O(nε) worst-case time and perform updates in O(nω(1,ε,1)−ε+n1+ε) worst-case time, for any ε∈[0,1], where ω(1,ε,1) is the exponent of the multiplication of an n × nε matrix by an nε × n matrix. The current best bounds on ω(1,ε,1) imply an O(n0.575) query time and an O(n1.575) update time in the worst case. Our subquadratic algorithm is randomized, and has one-sided error. As an application of this result, we show how to solve single-source reachability in O(n1.575) time per update and constant time per query.