Design a Lift Scheduler Service

Design a Solution Scheduler Service for a building with N floors (0 to N-1) and M lift cars.

Each lift navigates from one floor to another in 1 unit of time. You need to implement 2 APIs:

1. requestRide(fromFloor, toFloor): A passenger requests a ride from fromFloor to toFloor
2. nextAction(): Returns a list of states for each lift car. Valid states are:
   • UP: Lift moves up one floor
   • DOWN: Lift moves down one floor
   • OPEN_DOOR: Lift opens door for boarding/alighting
   • IDLE: Lift stays idle

Rules:

• All lifts start at floor 0
• nextAction() may be called at every time unit or sparsely
• Lifts have infinite capacity
• Loading and unloading passengers happens simultaneously during OPEN_DOOR
• Duplicate ride requests (same fromFloor and toFloor) should be ignored
• The scheduler should efficiently assign lifts to minimize wait time

Example: ` N = 3 floors, M = 2 lifts

1. requestRide(0, 2) // Passenger at floor 0 wants to go to floor 2
2. requestRide(1, 0) // Passenger at floor 1 wants to go to floor 0
3. nextAction() -> ["OPEN_DOOR", "UP"] // Lift 0 opens door at floor 0, Lift 1 goes up to floor 1
4. nextAction() -> ["UP", "OPEN_DOOR"] // Lift 0 goes up, Lift 1 opens door at floor 1
5. nextAction() -> ["OPEN_DOOR", "DOWN"] // Lift 0 at floor 2 opens door, Lift 1 goes down
6. nextAction() -> ["IDLE", "OPEN_DOOR"] // Lift 0 idle, Lift 1 at floor 0 opens door `

Methods

| Method | Parameters | Returns | Description | |--------|------------|---------|-------------| | requestRide | fromFloor, toFloor | None | Register a ride request from one floor to another | | nextAction | - | list | Return the next action for each lift (UP, DOWN, OPEN_DOOR, or IDLE) |