I always feel bad when I try out a new coding problem for interviews because I feel I'm going to offend candidates with such an easy problem (I interview mostly for senior positions). And I'm always shocked by how few are able to solve them. The current problem I use requires splitting a text into words as a first step. I show them the text, it's the entire text of a book, not just some simple sentence. I don't think I've had a single candidate do that correctly yet (most just split by a single space character even though they've seen it's a whole book with newlines, punctuation, quotes, parentheses, etc).