Question

This is an interview question & I’m looking wht experts can answer in a better way…

How do you sort an array containing million numbers in Java?

Thanks!

Answer 1

Interview questions never have the right answer.
The interviewers taught to ask open-end questions to see how you think and reason about problem.
You, in your turn, should show process of thinking and demonstrate that you can think in “software engineering way”.

Something like that:

1. Oh … 1 million numbers …
2. I think they are simple long so 1 million will take about 4 megabytes of memory
3. (Hm … might be I am wrong here and the long will take 8 bytes so it will be 8 Mbytes … – it’s not so important right now for that problem).
4. We are able to load it to the memory and use ready algorith Arrays.sort(long[])
5. (I do know my tools and core libs).
6. It will be no extra memory and O(n*log(n)) complexity (6 000 000 operations btw).
7. Can you do it faster ?
8. Oh … I remember that I heard about Radix sort – that algorithm gives us o(k*n) complexity where the k is number of significant ditigs (for long it will be twice as integer (2 billion = 9 digits) = 18 digits) so it will be 18 * 1 million = oh … it will be 3 times slower and I am not sure how much additional memory the algorithm will require.
9. If we have so much data that it will overflow the available memory?
10. We will chop data into l chunks size of m so each of chunks will fit into memory
11. We will sort each chunk separatedly and store results to files
12. Merging of sorted files will be with o(m) speed
13. And we will need to perform l-1 such merges
14. etc.