Yes, my personal preference is for recursion too - something very elegant and pleasing about it. Here I would probably go for the recursion + where query option.

For a programmer in a hurry, however, the brief non-recursive code might give a good trade-off between programming time and run time. It's certainly quite easy to understand and maintain.

Generally, I think this kind of talmudic debate is quite productive.
It explores the search space and the cost/benefits pretty thoroughly, and one finds things that one might otherwise have overlooked, and which might prove useful later ...

I look forward to the next one :-)

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