Manage robot factory settings.
When robots come off the factory floor, they have no name.
The first time you boot them up, a random name is generated in the format of two uppercase letters followed by three digits, such as RX837 or BC811.
Every once in a while we need to reset a robot to its factory settings, which means that their name gets wiped. The next time you ask, it will respond with a new random name.
The names must be random: they should not follow a predictable sequence. Random names means a risk of collisions. Your solution must ensure that every existing robot has a unique name.
See more at https://exercism.io/my/solutions/1f530c2e878949939311234b94e44ba1