Elevator, Floor, Request classes in LLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the Elevator class with a constructor.

LLD

class Elevator:
    def __init__(self, [1]):
        self.current_floor = 0
        self.requests = []

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

Afloors

Bid

Cspeed

Dcapacity

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'capacity' or 'speed' as the only constructor parameter.

The Elevator class constructor should take an identifier id to distinguish elevators.

2fill in blank

medium

Complete the code to add a method that adds a floor request to the elevator.

LLD

class Elevator:
    def add_request(self, [1]):
        self.requests.append(request)

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

Arequest

Bfloor_number

Cdestination

Dfloor

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'floor_number' or 'destination' which are not objects.

The method should accept a request object to add to the requests list.

3fill in blank

hard

Fix the error in the Floor class constructor parameter name.

LLD

class Floor:
    def __init__(self, [1]):
        self.number = number
        self.waiting_requests = []

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

Afloor_num

Bfloor

CfloorNumber

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using different parameter names than the assigned variable.

The parameter name should be number to match the assignment self.number = number.

4fill in blank

hard

Fill both blanks to complete the Request class with source and destination floors.

LLD

class Request:
    def __init__(self, [1], [2]):
        self.source = source
        self.destination = destination

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

Asource

Bdestination

Cstart

Dend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' or 'end' which do not match attribute names.

The constructor parameters should be source and destination to match the assignments.

5fill in blank

hard

Fill all three blanks to create a method that checks if the elevator is idle (no requests and at floor 0).

LLD

class Elevator:
    def is_idle(self):
        return len(self.[1]) == 0 and self.[2] == [3]

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

Arequests

Bcurrent_floor

C0

Dfloors

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'floors' or wrong attribute names.

The method checks if requests list is empty and current_floor is 0.

Practice

1. What is the primary role of the Request class in an elevator system?

easy

A. To store the floor number and direction of a user's request

B. To move the elevator between floors

C. To open and close the elevator doors

D. To track the number of elevators in the building

Solution

1. Step 1: Understand the purpose of Request class

   The Request class holds information about where a user wants to go and in which direction.

2. Step 2: Compare roles of other classes

   Elevator moves and Floor represents building levels, but Request stores user input details.

3. Final Answer:

   To store the floor number and direction of a user's request -> Option A

4. Quick Check:

   Request = user floor and direction [OK]

Hint: Request class holds user floor and direction info [OK]

Common Mistakes:

• Confusing Request with Elevator movement
• Thinking Request controls doors
• Mixing Request with Floor class responsibilities

2. Which of the following is the correct way to define a Request class constructor in Python to store floor and direction?

easy

A. def Request(floor, direction): self.floor = floor; self.direction = direction

B. def __init__(self, floor, direction): self.floor = floor; self.direction = direction

C. def __init__(floor, direction): self.floor = floor; self.direction = direction

D. def __init__(self): floor = None; direction = None

Solution

1. Step 1: Recall Python constructor syntax

   Python constructors use def __init__(self, ...) and assign attributes with self.attribute = value.

2. Step 2: Check each option

   def __init__(self, floor, direction): self.floor = floor; self.direction = direction correctly uses self and assigns floor and direction. Others miss self or parameters.

3. Final Answer:

   def __init__(self, floor, direction): self.floor = floor; self.direction = direction -> Option B

4. Quick Check:

   Constructor with self and attributes = def __init__(self, floor, direction): self.floor = floor; self.direction = direction [OK]

Hint: Python constructors need self parameter and attribute assignment [OK]

Common Mistakes:

• Omitting self parameter
• Using class name as constructor
• Not assigning attributes to self

3. Given this Python snippet, what will be printed?

class Request:
    def __init__(self, floor, direction):
        self.floor = floor
        self.direction = direction

r = Request(5, 'up')
print(r.floor, r.direction)

medium

A. Error: missing self

B. floor direction

C. 5 up

D. None None

Solution

1. Step 1: Understand object creation and attribute assignment

   The Request object r is created with floor=5 and direction='up'. These are stored in attributes.

2. Step 2: Print attributes

   Printing r.floor and r.direction outputs 5 and 'up' respectively.

3. Final Answer:

   5 up -> Option C

4. Quick Check:

   Attributes print as assigned = 5 up [OK]

Hint: Print object attributes to see stored values [OK]

Common Mistakes:

• Expecting attribute names instead of values
• Confusing class variables with instance variables
• Assuming error without checking code carefully

4. Identify the error in this Elevator class snippet:

class Elevator:
    def __init__(self, current_floor):
        self.current_floor = current_floor

    def move_to(self, floor):
        current_floor = floor

medium

A. Indentation error in move_to method

B. Missing return statement in move_to method

C. Constructor should not have parameters

D. The move_to method updates a local variable, not the elevator's floor

Solution

1. Step 1: Analyze move_to method

   The method assigns current_floor = floor without self., so it changes a local variable only.

2. Step 2: Understand instance variable update

   To update the elevator's floor, it should be self.current_floor = floor.

3. Final Answer:

   The move_to method updates a local variable, not the elevator's floor -> Option D

4. Quick Check:

   Missing self. means local variable used [OK]

Hint: Use self. to update instance variables inside methods [OK]

Common Mistakes:

• Forgetting self. prefix
• Thinking return is needed to update state
• Assuming indentation is wrong without checking

5. In designing an elevator system with Elevator, Floor, and Request classes, which approach best handles multiple simultaneous requests efficiently?

hard

A. Use a priority queue in Elevator to process requests by nearest floor and direction

B. Process requests in the order they arrive without sorting

C. Assign each request to a random elevator immediately

D. Ignore direction and always move elevators to the highest requested floor first

Solution

1. Step 1: Understand multiple request handling

   Efficient elevator systems prioritize requests to minimize travel and wait time.

2. Step 2: Evaluate options for request processing

   Using a priority queue to pick nearest floors and matching direction optimizes movement. Others cause inefficiency or randomness.

3. Final Answer:

   Use a priority queue in Elevator to process requests by nearest floor and direction -> Option A

4. Quick Check:

   Priority queue for nearest requests = Use a priority queue in Elevator to process requests by nearest floor and direction [OK]

Hint: Prioritize nearest requests with direction for efficient elevator movement [OK]

Common Mistakes:

• Ignoring direction leads to inefficient routes
• Random assignment causes delays
• Processing requests strictly by arrival order wastes time