I've been subscribed to Interview Cake for years, and today they had a really interesting question: Given a list of `n + 1`

integers in the range `1...n`

, find one of the duplicates (there is guaranteed to be at least one) in O(n) time and O(1) *additional* space. The answer is really interesting, and I recommend trying it, but I don't think it makes sense to care about additional space rather than total space, and I still think using a set is the best solution in practice.

# Additional space complexity isn't always a useful metric