Return a slice of the input in Rust
Rust interview exercise on Ownership & Borrowing, difficulty 1 of 3. Solve it in the editor beside a worked example, or cold in Interview mode with the example hidden; the tests run the moment you do.
Write first_word(s) that returns the first whitespace-separated word, or "" when there is none. Return a &str that borrows from s: no String, no allocation.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Interview mode hides the example: solve it from memory, without the hint or the solution, and it counts as solved cold. Progress is saved in your browser, and in your account if you sign in.