This problem has multiple solutions, as demonstrated by the HN comments. It's not asked to find a solution, instead to figure out your thought processes. You co

This problem has multiple solutions, as demonstrated by the HN comments. It's not asked to find a solution, instead to figure out your thought processes. You could come up with a comp sci solution (analogous to a data structure or algorithm), or a mathematical solution, or a physics solution or something different. You'd have to shape your answer to the position you're applying for. The article would be perfect for a programming position, above and beyond what I could ever hope to achieve.