[VA] Short & Sweet Math Challenges #23: "May the 4th Be With You !" Special

[Valentin Albillo]

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Hi, PeterP and Jeff 0.:

(05-24-2018 06:14 AM)PeterP Wrote:  Dear Valentin, thank you for providing yet another of your most wonderful teaching exercises!

Long time no see, PeterP !! I missed you ! ... Glad to see you taking part in one of my recent S&SMC's as you so frequently did in the past.

Quote:While it was more focused on 71B but you - thankfully - left one to be tackled by other calculators as well.

Yes, I was fearing that it was too 71B centric and regrettably the HP-71B seems placed in a no-man's land being the only calc-sized BASIC model, not RPN, not RPL, so it seems it's got very few fans and thus I provided a plan B by including last a challenge that could be solved in most calcs. My fears proved real so I'm glad I did.

Quote:upon finishing a working code discovered that I had found the original thread after the deadline had past (I did not read the fine print nor any of the comments lest I spoil my pleasure).

Actually, there are no hard deadlines, most especially for a challenge that no one posted anything about and thus for which I also posted no solution. In such a case anyone is welcome to post anything at any time.

Quote:My code takes a few minutes to deliver the first 9 digit 'Selfie' on my i41CX, is of course entirely clumsy and could use a true masters hand, but I wanted to ask for your opinion about posting it or not given that it is indeed past your suggested deadline.

See above. I'm eager to see your code so post it here at your earliest convenience, and if possible include timings.

Quote:In any case, I am very thankful for spending yet again an incredible amount of time and effort in concocting, creating, testing, and then wrapping in a nice story one of your wonderful S&SMC. Many more you make, I hope.

You're welcome, thanks a lot for your everlasting appreciation. I have several S&SMC plus assorted Mini-Challenges ready to post at a moment's notice.

Jeff O. Wrote:As a start, I went ahead and created a brute-force program with which I identified the 30 selfies from 1 to 10 digits:

I'm glad that you decided to give it a go, as you say you would. Brute-force or not your results are correct so congratulations, you're the first one (and so far the only one until PeterP posts his code) to solve it so my most sincere congratulations.

Quote:The above results were obtained running Free42 on my desktop PC. It produces the first 19 (i.e., 6-digit or fewer selfies) nearly instantaneously, then slows down considerably. [...] It looks like finding the seven 11-digit selfies would take about 20 days, so I think I’ll probably wait until I figure out some optimized method to find those rather than continuing to run my program.

Wise decision. Brute-force usually takes (generic) you so far, then you must think harder in order to beat the exponential curse.

Quote:In any case, a 10-fold or more increase in speed is really needed to make this practical. [...] I’ll keep thinking about the problem to see if I can develop a method that will be much quicker - hopefully it won’t keep me awake at night.

Please do. I'll post my original solution at 23:xx (GMT+1) next Sunday so you've got plenty of time to refine and expand your own.

Thanks to both and best regards.
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