Inverting Permutations In Place

Abstract

We address the problem of quickly inverting the standard representation of a permutation on $n$ elements in place. First, we present a naive algorithm to do it using $O(\log n)$ extra bits in $O(n^2)$ time in the worst case. We then improve that algorithm, using a small bit vector, to use $O(\sqrt n)$ extra bits in $O(n \sqrt n)$ time. Using a different approach, we present an algorithm to do it using $O(\sqrt n \log n)$ extra bits in $O(n \log n)$ time. Finally, for our main result, we present a technique that leads to an algorithm to invert the standard representation of a permutation using only $O(\log^2 n)$ extra bits of space in $O(n \log n)$ time in the worst case.