English

An in-place, subquadratic algorithm for permutation inversion

Data Structures and Algorithms 2020-04-22 v2

Abstract

We assume the permutation π\pi is given by an nn-element array in which the ii-th element denotes the value π(i)\pi(i). Constructing its inverse in-place (i.e. using O(logn)O(\log{n}) bits of additional memory) can be achieved in linear time with a simple algorithm. Limiting the numbers that can be stored in our array to the range [1...n][1...n] still allows a straightforward O(n2)O(n^2) time solution. The time complexity can be improved using randomization, but this only improves the expected, not the pessimistic running time. We present a deterministic algorithm that runs in O(n3/2)O(n^{3/2}) time.

Keywords

Cite

@article{arxiv.1901.01926,
  title  = {An in-place, subquadratic algorithm for permutation inversion},
  author = {Grzegorz Guśpiel},
  journal= {arXiv preprint arXiv:1901.01926},
  year   = {2020}
}
R2 v1 2026-06-23T07:05:00.832Z