Why elevator design tests state machines in LLD - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the initial state of the elevator.

LLD

elevator_state = '[1]'

Drag options to blanks, or click blank then click option'

ADOOR_OPEN

BMOVING

CIDLE

DMAINTENANCE

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing MOVING as initial state, which is incorrect because elevator starts idle.

The elevator starts in the IDLE state when it is not moving or opening doors.

2fill in blank

medium

Complete the code to transition the elevator state to moving when a request is received.

LLD

if request_received:
    elevator_state = '[1]'

Drag options to blanks, or click blank then click option'

AMOVING

BIDLE

CDOOR_OPEN

DSTOPPED

Attempts:

3 left

💡 Hint

Common Mistakes

Setting state to IDLE after request, which means no movement.

When a request is received, the elevator state changes to MOVING to reach the requested floor.

3fill in blank

hard

Fix the error in the state transition when the elevator reaches the floor.

LLD

if elevator_state == 'MOVING' and at_floor:
    elevator_state = '[1]'

Drag options to blanks, or click blank then click option'

AMOVING

BIDLE

CMAINTENANCE

DDOOR_OPEN

Attempts:

3 left

💡 Hint

Common Mistakes

Setting state to IDLE immediately, skipping door opening.

When the elevator reaches the floor, it should open the door, so the state changes to DOOR_OPEN.

4fill in blank

hard

Fill both blanks to complete the state machine transition for closing doors and going idle.

LLD

if elevator_state == 'DOOR_OPEN' and door_closed:
    elevator_state = '[1]'
if elevator_state == '[2]' and no_requests:
    elevator_state = 'IDLE'

Drag options to blanks, or click blank then click option'

AMOVING

BDOOR_OPEN

CIDLE

DSTOPPED

Attempts:

3 left

💡 Hint

Common Mistakes

Setting state to IDLE immediately after door closes without checking requests.

After doors close, elevator moves if there are requests; if no requests, it goes idle.

5fill in blank

hard

Fill all three blanks to complete the dictionary for elevator states and their descriptions.

LLD

state_descriptions = {
    '[1]': 'Elevator is idle and waiting',
    '[2]': 'Elevator is moving between floors',
    '[3]': 'Elevator doors are open'
}

Drag options to blanks, or click blank then click option'

AIDLE

BMOVING

CDOOR_OPEN

DMAINTENANCE

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up state names and descriptions.

The dictionary maps elevator states to their human-readable descriptions.