Generic group_by in Rust
Rust interview exercise on Traits & Generics, difficulty 3 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 group_by(items, key) that groups clones of the items by whatever key(&item) returns, keeping input order inside each group. K needs Ord because the result is a BTreeMap; T needs Clone because the input is only borrowed.
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.