I'm nearly convinced that eliminating duplicates while sorting ...leads to O(D*log(U)) performance.

Do you have an algorithm in mind? One that is compatible with a file-based merge sort?

I guess if you:

  1. Sort a buffer full; write to spill file eliminating dups as you go; repeat till input read.
  2. Parallel read from spill files, again eliminating dups as you go; until output written.

Then you'd get: O( N/S log N/S * S) + the merge.

So for 10e6 (I'm using log10 instead of log2 for easy math):

Of course, the merge step gets more expensive the more files you have. It is at least O(N/S log S) regardless of the ratio of U to N, so I don't think that you are going to approach O(N log U). Much less O(D Log U).

In reply to Re^8: In-place sort with order assignment (dumb) by BrowserUk
in thread In-place sort with order assignment by BrowserUk

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