Restaurant, Menu, Order classes in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Identify the correct relationship between Restaurant, Menu, and Order classes

Which option correctly describes the relationship between Restaurant, Menu, and Order classes in a typical system design?

A A Restaurant has multiple Menus, and each Order is linked to one Menu item.

B An Order has multiple Menus, and each Restaurant contains one Order.

C A Menu contains multiple Orders, and each Restaurant is linked to one Order.

D An Order contains multiple Restaurants, and each Menu belongs to one Order.

💡 Hint

Think about how a restaurant offers menus and customers place orders from those menus.

A Restaurant typically offers multiple Menus (e.g., breakfast, lunch). Each Order is placed for items from a Menu. So, the Restaurant owns Menus, and Orders reference Menu items.

❓ Architecture

intermediate

Choose the best class design for handling multiple orders in a restaurant system

Which class design best supports managing multiple orders simultaneously in a restaurant system?

A Menu class holds a list of Order objects, and Restaurant class holds a single Order object.

B Menu class holds a list of Restaurant objects and a list of Order objects.

C Order class holds a list of Restaurant objects and a list of Menu objects.

D Restaurant class holds a list of Menu objects and a list of Order objects.

💡 Hint

Consider where orders should be tracked and how menus relate to restaurants.

The Restaurant class should manage its Menus and track all Orders placed. Menus do not own Restaurants or Orders. Orders belong to Restaurants and reference Menu items.

❓ scaling

advanced

Scaling the Order processing for a high-traffic restaurant system

What is the best approach to scale order processing when a restaurant receives thousands of orders per minute?

A Store all orders in memory within the Menu class for faster access.

B Process all orders synchronously in the Restaurant class to maintain consistency.

C Use a message queue to asynchronously process orders and update the database.

D Limit the number of orders accepted by rejecting excess orders immediately.

💡 Hint

Think about how to handle many requests without blocking the system.

Using a message queue allows the system to accept orders quickly and process them asynchronously, improving scalability and reliability.

❓ tradeoff

advanced

Tradeoff between storing Menu items in Order vs referencing Menu items

What is the main tradeoff when choosing between storing full Menu item details inside an Order versus storing only references to Menu items?

A Storing full details increases data duplication but preserves order history accurately if Menu changes.

B Storing references reduces data duplication but risks order data inconsistency if Menu items change.

C Both approaches have no impact on data consistency or storage requirements.

D Storing references increases storage size and makes order retrieval slower.

💡 Hint

Consider what happens if the Menu changes after an order is placed.

Storing full Menu details in the Order preserves the exact items ordered even if the Menu changes later, but it duplicates data. Storing references saves space but risks inconsistency.

❓ component

expert

Estimate the capacity needed for order storage in a restaurant system

A restaurant expects to receive 10,000 orders daily. Each order stores 5 menu items on average. Each menu item detail stored in an order requires 1 KB of storage. Estimate the total storage needed for order data for one year.

A Approximately 1.825 GB

B Approximately 18.25 GB

C Approximately 182.5 GB

D Approximately 0.1825 GB

💡 Hint

Calculate daily storage then multiply by 365 days.

Daily storage = 10,000 orders * 5 items * 1 KB = 50,000 KB = 50 MB. Yearly storage = 50 MB * 365 = 18,250 MB = 18.25 GB.

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