I don’t mean to be rude, but there’s no non-obvious “algorithm” for reversing a linked list in-place. If you can keep the details straight, you’re done. If a candidate had trouble with this problem, that would tell me that either 1) they have difficulty working at a fine level of detail, or 2) they aren’t comfortable with pointers. Either possibility is problematic for jobs that require attention to low-level detail or manipulating pointers or references.