Not being able to walk a linked list sounds pretty dire. Is it possible that candidate A hadn't written tree-walking code recently? Did he have access to reference materials?
I aced my CS degree, but a few years later, after endless CRUD, I was given a task at work which involved constructing and analyzing hierarchical data. After realizing that it would be modelled with a tree, and a few minutes with my textbook and it all came back to me. If I had been given the same task in an interview, I may well have flunked it.
I personally allow candidates access to Google and whatever else they need on programming tests. That's how they'd solve problems in real life, so why make them relive their final college exams in an interview?
I aced my CS degree, but a few years later, after endless CRUD, I was given a task at work which involved constructing and analyzing hierarchical data. After realizing that it would be modelled with a tree, and a few minutes with my textbook and it all came back to me. If I had been given the same task in an interview, I may well have flunked it.
I personally allow candidates access to Google and whatever else they need on programming tests. That's how they'd solve problems in real life, so why make them relive their final college exams in an interview?