The performance of this is N ** 2 + NM (where N is the size of s2 and M is the size of s1) since:

• it loops through all the characters of s2 (N)
• for each of those caracters it counts the time the character 'x' appears. For that it has to loop through all s2 (N) and s1 (M)

That's far from ideal, which should be N + M

Thank you for this comment rsrs. I started to study this year and I was looking and wondering why people were converting to strings and than back to integer

uniq method isn't needed

Each time its 5 times less code than mine :D

I'd love to know how this works too.

Wow, recursion (not even tail) is "best practice" vs iteration? What is the world rolling to?

It's nice, I had similar solution, but even now I cannot pass performance tests with it.

Fails the "performance matters" test.

Is using recursion best practices when there are other, reasonably consise ways to do it? The context im thinking of is best practices as a web dev.

cool