Your question is SRE Coding Challenge. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
The coding challenge was through Hacker Rank and a pretty typical SRE coding challenge. Not too deep on the algorithms side, but be prepared for refactoring and understanding the big O of the solution.