I tried very hard and gave up after a full day. I am now looking at some clever solutions and I don't get them all. Would love to learn from my mistakes. Are there any ressources you can recommend? Or is there anyone that would care to explain?

That's beautiful. Care to explain? I only came up with an abomination of a thousand if-clauses that timed out on the large test cases. Much appreciated!

I don't think it's particularly good practice to modify built-in prototypes. You risk breaking changes in the future.

Personally, I find loops harder to read and just as error prone as regular expressions. And it's a nice opportunity to practice them regexes :)

Same in R, if I'm not mistaken.

Same here. It works but is so ugly I dubbed the result to return "ihatemycode" since i get sick of even looking at it. Sadly, it performs too bad and gets killed by timeout. Therefore, nobody will ever have to look at it.

That makes sense. Thank you!