Does anyone know how to pre-processes N to make those queries in O(1) time because this would be ideal.

Not possible. At least not without infinite memory capacity.

About the best you could do is create a hash or bit-vector from the larger of the two intervals suitably adjusted (+/-Z), so that you can do O(1) lookups of the values in the smaller interval, within that.

If you can arrange to deal with all the Z=x in one pass and Z=y in the next and so on, then you could build a suitably adjusted array the same size as the original from which you can build your lookup hashes/vectors for each new range pair, but its unlikely to make a huge difference.

The lookup removes one level of nested loop from the problem, but I see no way of reducing the others.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

The start of some sanity?

In reply to Re: Computing array intersections by BrowserUk
in thread Computing array intersections by baxy77bax

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