Scrupuli

I have been working my way through some fun problems at Project Euler.net. Fun for me, anyway. To solve them takes what Edsger Dijkstra called mathematical engineering: mathematics and programming skills used together.

There are many problems to choose from, from very easy to very challenging. But they all have this in common: though it takes time and thought to analyze each problem, the solution should run on any basic computer in less than a minute.

Which is great! It means that nobody needs a supercomputer to solve these problems: just a PC and the will to learn and succeed.

Which brings me to Problem 34, find the sum of all numbers which are equal to the sum of the factorial of their digits. This problem is eating my lunch.

My solutions to problems 1–33 were sometimes lazy. Yes, some run under a millisecond, or scale to much bigger problems than those posed … but I have also been perfectly satisfied with brute force solutions if they ran under a minute on my old PC.

But, so far, my solution to Problem 34 takes more than 2 minutes to run and its output is rejected by Project Euler for no good reason that I can see. Suddenly I cannot afford to be lazy.

Incidentally, all my solutions are written in Perl. I have, as I hoped, learned quite a bit about optimizing Perl programs that I did not know before.

In case you can’t tell, I am really enjoying this!