This was an assignment of the Operating Systems course in Fall 2020 at Shahid Beheshti university.
Doctors-Building is compeletly similar to Sleeping Barber problem which is a classic inter-process communication and synchronization problem between multiple operating system processes. The problem is analogous to that of keeping a barber working when there are customers, resting when there are none, and doing so in an orderly manner.
Here the doctors are the same as barbers and the patients are the same as customers in the sleeping barber problem. In order to get more information about the defintion and extra explaination of the Sleeping Barber problem you can visit wikipedia.