Trading Space for Time in Undirected $s-t$ Connectivity

  • Authors:
  • Andrei Z. Broder;Anna R. Karlin;Prabhakar Raghavan

  • Affiliations:
  • -;-;-

  • Venue:
  • SIAM Journal on Computing
  • Year:
  • 1994

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Abstract

Aleliunas et al. [20th Annual Symposium on Foundations of Computer Science, IEEE Computer Society Press, Los Alamitos, CA, 1979, pp. 218--223] posed the following question: "The reachability problem for undirected graphs can be solved in log space and $O(mn)$ time [$m$ is the number of edges and $n$ is the number of vertices] by a probabilistic algorithm that simulates a random walk, or in linear time and space by a conventional deterministic graph traversal algorithm. Is there a spectrum of time-space trade-offs between these extremes?" This question is answered in the affirmative for sparse graphs by presentation of an algorithm that is faster than the random walk by a factor essentially proportional to the size of its workspace. For denser graphs, this algorithm is faster than the random walk but the speed-up factor is smaller.