An excellent point. Though for the scope of the problem it would hardly matter.

You don't need the extra parentheses if you wanted a cleaner oneliner

if there's an x in the string, then the input is invalid

Given a string made up of letters a, b, and/or c

good, but if input string have a "x" char this solution doesnt worked.

best.
very clever and clean => best practice 👍

100% it is a best variant, geez, genius and minimalistic

I didn't even think of that. I used if

Approved some time ago

• Updated Rust version to latest
• Slightly improved failure messages

Please update the rust version.

You have to look for harshad numbers, where the product of "sum of digits" and "sum of digits"[::-1] is the number again. Now lets have a look at the sum of digits.

9: you need at least 1 digit to get this. And 9 * 9 = 81 (2 digits). No problem.

99: you need at least 11 digits to get this. And 99 * 99 is < 10.000 (4 digits). For bigger numbers this is getting worse, so the matching harshad numbers are below 10.000. And there we have just these four numbers...

the test cases weren't long enough I guess

Oh for Pete's sake... :)

Easy to read. Nice logic.

Since Option implements IntoIterator you could use "Some('_')" instead of "std::iter::once('_')"