Elevators - Simulate and Optimize Elevator Scheduling

Question

## Round 1 - Coding / OOD

## Problem

Design an elevator controller for a building with `n` floors and `k` elevators. Requests arrive as `(floor, direction)` pairs. Implement a scheduling policy that minimizes average wait time.

```python
class ElevatorState:
    current_floor: int
    direction: str  # "UP", "DOWN", or "IDLE"
    stops: list[int]

class ElevatorController:
    def __init__(self, num_floors: int, num_elevators: int): ...

def request(self, floor: int, direction: str) -> None:
        # Called when a user presses the UP or DOWN button
        ...

def step(self) -> None:
        # Advance simulation by one time unit
        ...

def get_states(self) -> list[ElevatorState]: ...
```

```
Example:
ctrl = ElevatorController(num_floors=10, num_elevators=2)
ctrl.request(floor=3, direction="UP")
ctrl.request(floor=7, direction="DOWN")
ctrl.step()  # elevator 0 moves toward floor 3
ctrl.get_states() -> [ElevatorState(floor=1, dir="UP", stops=[3]), ...]
```

## Follow-ups

1. Describe the SCAN (elevator) algorithm. What are its weaknesses?
2. How would you handle a destination-dispatch system where users input the target floor before boarding?
3. How would you model peak-hour load (e.g. morning rush to floor 1)?
4. How does adding priority (e.g. freight elevator) change your design?

Elevators - Simulate and Optimize Elevator Scheduling

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