some c# coding practices for IV

These questions will seldom hit the phone round...

Q: Implement IEnumerable<string> foo(IEnumerable<string> aa, IEnumerable<string> b) such that foo returns string in either aa or b but not both.

To keep things simple, let's assume aa holds unique elements, and b too.

Q: regex engine supporting quantifier "*", and the wild-card "."
Q: IteratorTest from MS
Q: circular buffer
Q: reverse a linked list in-place
Q: rotate a long array by 3
Q: spreadsheet concretization

(610610 blog has a letter to XR, which shows a list of coding practice projects I completed.)