Format a duration in Rust
Rust interview exercise on Practical, 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 format_duration(total_seconds) as "M:SS", or "H:MM:SS" once there is at least an hour. Minutes and seconds are zero-padded to two digits except the leading unit.
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.