[sova]

It depends on the complexity, which language(s) you are using, and how you will parse the search string (which Context Free Grammar it will obey). Just recently, this was a task for me that ended up landing me an interview. A take-home problem. Even a simple search engine needs some clever reverse-indexing for speed. Add any sort of logic like And or OR that not even Google implements and now your parser has to work, and you have to be able to translate from tokenized parse tree with operators to results. It's a great learning exercise for someone with experience, initiative, and enough background with CFG parsing, building a reverse index, and set logic -- but without some key Computer Science building blocks it would end up being quite a challenge.