DEVELOPER CODING EXERCISE

Model an Elevator System

###Features:

1. Each elevator should be able to report what floor it is on, whether it is moving, and what floor it is going to next. It should also report what floors passengers have requested. NOTE: This information is accesible directly from properties:

   elevator.currentFloor;
   elevator.isMoving;
   elevator.destinationFloor;
   elevator.floorRequests;
   

2. The Elevator System should be able to accept a service request from any floor, and select only one elevator to respond to it. The selection algorithm should be reasonable.

3. Each elevator should be able to respond to a service request from a floor (via #2) and move towards that floor.

NOTE: Because physical implementation of this system would take time for elevators to move from one floor to the other, I invision the coded implementation using a step system where elevators spend 1 step per floor and 0 steps to load and unload passengers.

4. Each elevator should be able to respond to floor requests from passengers inside the elevator.

NOTE: This is called by the elevator since these buttons exist inside the elevator car.

5. Each elevator should be able to deal with both a service request and a floor request at the same time and decide what floor to go to next.

NOTE: Because destination is set programatically at the end of a service request or floor request, whichever function finishes first will inevitably update the destination first. Both of these functions will update destination accordingly based on direction - that is to say that if we are going up, and a floor or service request is placed above our current destination, then the destination will be updated to the higher floor.

6. Each elevator should keep track of how many floors it has travelled over time. Again accessible via properties:

elevator.totalFloorsTravelled;

7. The Elevator System should keep track of how many service requests it has processed from people wanting an elevator.

elevatorSystem.totalServiceRequests;

8. An elevator should be able to be put into 'Maintenance Mode' where it no longer responds to service requests and waits at floor 1. The Elevator System should handle this gracefully and send all requests to the functioning elevator, or do nothing in both elevators are in Maintenance Mode.

NOTE: For the sake of time, my implementation drops all floor requests and current destinations from an elevator upon toggling Maintenance Mode. This can be remedied, but would take extra time to implement.

9. The Elevator System should function for 3 elevators and have all of the above functionality.

10. The Elevator System should function for any number of elevators and have all of the above functionality. See:

    - (void)addElevator;