find if two arrays contain the same set of integers without extra space and faster than NlogN

Question

I came across this post, which reports the following interview question:

Given two arrays of numbers, find if each of the two arrays have the same s

Answer 1

You can break the O(n*log(n)) barrier if you have some restrictions on the range of numbers. But it's not possible to do this if you cannot use any extra memory (you need really silly restrictions to be able to do that).

I would also like to note that even O(nlog(n)) with sorting is not trivial if you have O(1) space limit as merge sort uses O(n) space and quicksort (which is not even strict o(nlog(n)) needs O(log(n)) space for the stack. You have to use heapsort or smoothsort.

Some companies like to ask questions which cannot be solved and I think it is a good practice, as a programmer you have to know both what's possible and how to code it and also know what are the limits so you don't waste your time on something that's not doable.

Check this question for a couple of good techniques to use: Algorithm to tell if two arrays have identical members