The design of the system is split among two classes - Elevator and ECS (Elevator Control System). The Elevator class models each elevator and ECS class models the system as a whole. APIs are exposed by the ECS class and clients interact with the system through those APIs.

The crux of the design is in the Scheduling Algorithm in ECS class where new pickup requests are assigned to nearest elevators. The destination floors are assigned to min heap in case the elevator is going UP and are assigned to a max heap in case the elevators are going DOWN.

This system does not work in an FCFS schedule. It assigns the elevator that is closest to the requested pickup floor.

A pickup request consists of two integers - floor and destination floor. Direction is not required as the system deduces this automatically through the request.

The interface is modified from the actual specification. The update method has been removed as clients should not be handed control over modification of the elevator statuses. The rest of the methods are the same.

def status(self):
    # Returns a list of 3-tuple status for each elevator

def pickup(self, floor_no, goal_floor_no):
    # Issue a pickup request from a floor_no to a goal_floor_no

def step(ecs):
    # Simulate the functioning of ecs based on the command file

• enum34 version 1.1.6 => $ pip install enum34
• heapq_max version 0.21 => $ pip install heapq_max

• Add possible commands to the commands file
• Format :
  • start max_elevators
  • status
  • pickup floor_no goal_floor_no
• Example

start 10
status
pickup 1 10
step
step
pickup 2 10
step
step
step
step
step
step
pickup 10 5
step
pickup 8 5
step
step
step
step
pickup 7 10
step
step
step
step
step
status
pickup 6 10
step
step
step
step
step
step
step
step
pickup 1 10
status

• Run through $ python setup.py commands

• The elevator control system does not consider the capacity of the elevator when processing a new pickup request.
• Theoritically, there is a possibility of starvation in the system. To see this, consider a building with one elevator and infinite floors. The first person that gets in, goes up and the elevator keeps getting a pickup request for further up top. In such a case, a request from a lower floor will be waiting in the system's queue and will never be assigned to an elevator.
• Dynamic reconfiguration of elevators and the pickup queue. Suppose an elevator is not considered as nearest at some point for a certain pickup request at that point in time. Since it's moving, a few seconds later it's nearer than the one that was scheduled for the pickup of that request.