I'd rather not post too many details about the particular question, but it's only slightly more complex than String#split. It has multiple valid solutions, from regex matching to for/while/do&while loops to String#substring. If you have even a basic understanding of your language of choice's standard library, at least one solution is obvious and implementable within minutes.

I'd say about half of the candidates that interview are unfamiliar with the String#substring equivalent of their language. This is for a senior position, and everyone has multiple years of experience on their resume. It's... interesting.