[Solved] In this elevator state machine code, what is the bug causing the elevator to never open doors?... In this elevator state machine code, what is the bug causing the elevator to never open doors? | LLD

LLD - Design — Elevator System

In this elevator state machine code, what is the bug causing the elevator to never open doors?

current_state = 'Idle'

def callElevator():
    global current_state
    if current_state == 'Idle':
        current_state = 'Moving'

def arriveFloor():
    global current_state
    if current_state == 'Moving':
        current_state = 'Idle'  # Bug here

def openDoor():
    global current_state
    if current_state == 'DoorOpen':
        current_state = 'Idle'

Acurrent_state is not initialized

BcallElevator() does not change state

CopenDoor() changes state incorrectly

DarriveFloor() sets state to 'Idle' instead of 'DoorOpen'

Step-by-Step Solution

Solution:

Step 1: Analyze arriveFloor() function
arriveFloor() changes 'Moving' state directly to 'Idle', skipping 'DoorOpen'.
Step 2: Understand effect on door opening
Since state never becomes 'DoorOpen', openDoor() condition never triggers, so doors never open.
Final Answer:
arriveFloor() sets state to 'Idle' instead of 'DoorOpen' -> Option D
Quick Check:
arriveFloor() wrong state change = no door open [OK]

Quick Trick: Check if all states are reachable in transitions [OK]

Common Mistakes:

MISTAKES

Ignoring wrong state assignment
Assuming callElevator() is faulty
Overlooking openDoor() condition

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In this elevator state machine code, what is the bug causing the elevator to never open doors?

Step 1: Analyze arriveFloor() function

Step 2: Understand effect on door opening

Final Answer:

Quick Check:

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