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Gerald H · 07-09-2017, 06:49 PM

(07-09-2017 03:33 PM)DavidM Wrote:
(07-09-2017 10:49 AM)Gilles59 Wrote: David, I like very much your approach. You can easily save 2.5 Bytes at the end with :

Code:

OVER instead of DUP UNROT
In this specific case, the result will be the same

Thanks, Gilles. I'm not clear on exactly what you're suggesting, though. If I replace "DUP UNROT" with a single "OVER", the only time it will give a correct answer for all-odd-digit input is if the input only consists of 1s. As an example, 13579 is all-odd, but results in 0 under those conditions. So I must be misunderstanding what you meant.

I did ultimately decide to make a change to those two commands, though, as I think "SWAP OVER" is clearer in hindsight (though it's the same speed/size as before).

The most "expensive" part of my approach (in terms of speed) is in creating the mask. I kept thinking that there must be a better (built-in) way, and there probably is. But I gave up looking and decided to create a command (RPTCHR) that fulfills that purpose. It's similar to this program that Gerald posted, but more generic in that the repeated character is supplied as a parameter.

Though I consider it to be out-of-scope for this challenge, using RPTCHR to generate the mask made my test both smaller and faster, resulting in a score of about 2.2 (RPTCHR is wicked fast).

A quick scan of the submissions here shows that we're all approaching this using algorithms that check each individual digit for odd/even status. I keep thinking, though, that there might be some kind of mathematical approach that could be applied instead. I've looked at congruences, GCD, and a couple other experiments trying to find some combination of steps that might work here, but I'm afraid I lack the mathematical knowledge to find that kind of solution. Has anyone had any success using something other than a check-every-digit type of approach?

I'd love to be corrected, but my limited knowledge of numbers says that the parity of a digit in a number other than the final position contains no particular info concerning the whole number, ie individual digit checking is the only method.