In my interview for my current job, I was asked to implement an algorithm that finds the edit distance between two strings. This is a classic algorithm, one that I had learned and implemented about a year before in my algorithms class, and loved for its utility, but I could not remember a specific little detail!

However, neither did my interviewers! So we worked together trying to re-derive the algorithm from the problem, the expected output, and the rough idea of how it worked. We did not succeed, but we did demonstrate an ability to work through things together, an ability to stand up and point out incorrect things, an ability to reason through a problem, etc. I got the job.