In-Memory DB with per-key user lock: setByUser/deleteByUser/lock/unlock

Problem: In-Memory DB Variant — Add User-based locking You are implementing a simplified in-memory database storing key -> record. This variant introduces users and a lock mechanism per key/record. Locking rules A key can be locked by a user. The user holding the lock can modify the data for that key. Any non-lock-holding user must not be allowed to modify that key (the operation should fail / be rejected as specified). Functions to implement (at least) Implement the following operations (exact signatures/return values are defined by the OA): setByUser(user, key, ...) deleteByUser(user, key, ...) lock(user, key) unlock(user, key) Output/Return Return the required status for lock/unlock and for modification attempts without proper lock ownership. Constraints / edge cases (per OA) Behavior when key does not exist. Re-locking by the same user. Unlock attempts by non-owner. Whether there is a wait queue, re-entrant locks, expiry, etc. Note: The original post only captures the core idea; the full I/O format and edge conditions are not included. Follow the OA statement. Example Input N/A (depends on OA command format) Output N/A