Restaurant, Menu, Order classes in LLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the Restaurant class with a name attribute.

LLD

class Restaurant:
    def __init__(self, [1]):
        self.name = name

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

Aname

Blocation

Corder

Dmenu

Attempts:

3 left

💡 Hint

Common Mistakes

Using unrelated parameter names like menu or order.

The constructor needs a parameter name to set the restaurant's name.

2fill in blank

medium

Complete the code to add a method that adds a Menu item to the Restaurant.

LLD

class Restaurant:
    def __init__(self, name):
        self.name = name
        self.menu_items = []

    def [1](self, item):
        self.menu_items.append(item)

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

Aadd_menu_item

Bremove_menu_item

Cget_menu

Dupdate_menu

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names that do not add items like remove or get.

The method to add a menu item should be named add_menu_item to clearly describe its purpose.

3fill in blank

hard

Fix the error in the Order class constructor to correctly initialize the order_id attribute.

LLD

class Order:
    def __init__(self, [1]):
        self.order_id = order_id
        self.items = []

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

Aitems

Border_id

Cid

Dorder

Attempts:

3 left

💡 Hint

Common Mistakes

Using a parameter name different from the attribute name causing errors.

The constructor must accept order_id as a parameter to initialize the attribute.

4fill in blank

hard

Fill both blanks to create a method in Order that adds a Menu item to the items list.

LLD

class Order:
    def __init__(self, order_id):
        self.order_id = order_id
        self.items = []

    def [1](self, [2]):
        self.items.append(item)

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

Aadd_item

Bitem

Cremove_item

Dorder

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong method names or parameter names that don't match the code.

The method should be named add_item and take a parameter item to add to the order.

5fill in blank

hard

Fill all three blanks to create a method in Menu that returns a dictionary of item names and prices for items priced above a threshold.

LLD

class Menu:
    def __init__(self):
        self.items = {}

    def get_expensive_items(self, price_threshold):
        return {name: [1] for name, [2] in self.items.items() if [3] > price_threshold}

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

Aprice

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names or mixing keys and values.

The dictionary comprehension uses price as the value, iterates over price pairs, and compares price to the threshold.

Practice

1. Which class should primarily hold the list of available food items and their prices in a restaurant system?

easy

A. Restaurant

B. Menu

C. Order

D. Customer

Solution

1. Step 1: Understand the role of Menu class

   The Menu class is designed to store food items and their prices, acting as the restaurant's catalog.

2. Step 2: Differentiate from other classes

   Order tracks customer requests, Restaurant manages overall operations, Customer represents the diner. Only Menu holds items and prices.

3. Final Answer:

   Menu -> Option B

4. Quick Check:

   Menu = items and prices [OK]

Hint: Menu holds items and prices, not orders or customers [OK]

Common Mistakes:

• Confusing Order with Menu
• Thinking Restaurant holds item prices
• Assuming Customer stores menu data

2. Which of the following is the correct way to add a new item to the Menu class in a typical object-oriented design?

easy

A. menu.addItem('Pizza', 12.99)

B. Menu.add('Pizza', 12.99)

C. menu.insertItem('Pizza', 12.99)

D. addItem(menu, 'Pizza', 12.99)

Solution

1. Step 1: Identify instance method usage

   Adding an item to a Menu instance uses the instance method, so calling menu.addItem(...) is correct.

2. Step 2: Eliminate incorrect syntax

   Menu.add(...) suggests a static method which is unlikely; insertItem is not standard; addItem(menu, ...) is procedural, not OOP style.

3. Final Answer:

   menu.addItem('Pizza', 12.99) -> Option A

4. Quick Check:

   Instance method call = menu.addItem(...) [OK]

Hint: Use instance.method() to add items, not static or procedural calls [OK]

Common Mistakes:

• Using static method call instead of instance method
• Confusing method names
• Calling functions outside class context

3. Given the following code snippet, what will be the total cost of the order?

menu = Menu()
menu.addItem('Burger', 5.0)
menu.addItem('Fries', 2.5)
order = Order(menu)
order.addItem('Burger', 2)
order.addItem('Fries', 3)
total = order.calculateTotal()

medium

A. 17.5

B. 15.0

C. 20.0

D. 12.5

Solution

1. Step 1: Calculate cost for each item

   Burger price is 5.0, quantity 2 -> 5.0 * 2 = 10.0; Fries price is 2.5, quantity 3 -> 2.5 * 3 = 7.5.

2. Step 2: Sum the costs

   Total cost = 10.0 + 7.5 = 17.5.

3. Final Answer:

   17.5 -> Option A

4. Quick Check:

   (5*2)+(2.5*3) = 17.5 [OK]

Hint: Multiply price by quantity, then add all items [OK]

Common Mistakes:

• Adding quantities instead of multiplying by price
• Forgetting to multiply price by quantity
• Mixing up item prices

4. In a system where the Order class adds items without checking the Menu, what is the main issue that can occur?

medium

A. Order will reject all items by default

B. Menu prices will automatically update in Order

C. Order may include items not available in the Menu

D. Restaurant will close automatically

Solution

1. Step 1: Understand the role of validation

   Order should verify items exist in Menu to avoid invalid orders.

2. Step 2: Identify consequence of missing check

   Without checking, Order can contain items not on Menu, causing errors or confusion.

3. Final Answer:

   Order may include items not available in the Menu -> Option C

4. Quick Check:

   Missing validation = invalid items in Order [OK]

Hint: Always check Menu before adding items to Order [OK]

Common Mistakes:

• Assuming automatic price updates
• Thinking Order rejects items by default
• Confusing system behavior with unrelated effects

5. How would you design the Order class to handle multiple orders from different customers simultaneously in a scalable restaurant system?

hard

A. Store all orders in a single list without identifiers

B. Keep orders only in memory without persistence

C. Allow only one order at a time to avoid conflicts

D. Use unique order IDs and store orders in a centralized database with concurrency control

Solution

1. Step 1: Identify need for unique order tracking

   Each order must have a unique ID to distinguish between multiple customers' orders.

2. Step 2: Ensure scalability and data integrity

   Storing orders in a centralized database with concurrency control allows multiple orders simultaneously without conflicts.

3. Final Answer:

   Use unique order IDs and store orders in a centralized database with concurrency control -> Option D

4. Quick Check:

   Unique IDs + concurrency = scalable order handling [OK]

Hint: Use unique IDs and concurrency-safe storage for multiple orders [OK]

Common Mistakes:

• Ignoring concurrency issues
• Using single list causing data overwrite
• Not persisting orders leads to data loss