Subquadratic algorithms for 3SUM

  • Authors:
  • Ilya Baran;Erik D. Demaine;Mihai Pǎtraşcu

  • Affiliations:
  • MIT Computer Science and Artificial Intelligence Laboratory;MIT Computer Science and Artificial Intelligence Laboratory;MIT Computer Science and Artificial Intelligence Laboratory

  • Venue:
  • WADS'05 Proceedings of the 9th international conference on Algorithms and Data Structures
  • Year:
  • 2005

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Abstract

We obtain subquadratic algorithms for 3SUM on integers and rationals in several models. On a standard word RAM with w-bit words, we obtain a running time of O(n2 / max{$\frac{w}{lg^2 w}, \frac{lg^2 n}{(lg lg n)^2}$}). In the circuit RAM with one nonstandard AC0 operation, we obtain O(n2 /$\frac{w}{lg^2 w}$). In external memory, we achieve O(n2 / (MB)), even under the standard assumption of data indivisibility. Cache-obliviously, we obtain a running time of O(n2 / $\frac{MB}{lg^2 M}$). In all cases, our speedup is almost quadratic in the parallelism the model can afford, which may be the best possible. Our algorithms are Las Vegas randomized; time bounds hold in expectation, and in most cases, with high probability.