Requirement

Locker

Locker has an init capacity that won't be changed after it has been produced.
Assuming the capacity of the locker is n, the label of boxes will be from 1 to n.
When user requests an empty box, it will provide a box with the minimal label from all empty boxes.
After providing user a box, it will give user a ticket with the box label and record the timestamp. After this the box is unavailable to other users.
When user returns the box, user should provide the ticket. The ticket label and timestamp should both match the system record. If so the box will open.
If the locker is full, and a user requests a box, it will print an error message "Sorry, this locker is full.".
Locker should has a name or id.