Did you solve it? Do you think like a software engineer?

The answer to today's tantalising tech teaser

Earlier today I set you the following puzzle, a classic interview question for software engineers. It seems really to have caught your imaginations: so far the original article has had almost 500 below-the-line comments. Many are lateral takes on the problem, often humorous. Many are meditations on the ambiguities involved when phrasing a technical question about data structures in a fantasy setting. Some are furious posts about what makes a spoiler, and some are celebrations of your favourite software engineers.

Enough already, here is the puzzle again, together with the solution.