DRY (Don't Repeat Yourself) in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why is DRY important in system design?

Imagine you are designing a system with multiple modules that share similar logic. Why should you apply the DRY principle?

A To reduce code duplication and make maintenance easier

B To increase the number of lines of code for clarity

C To make each module completely independent with no shared code

D To add more comments explaining repeated code

💡 Hint

Think about how repeating the same code affects fixing bugs or adding features.

DRY helps avoid repeating code so that changes need to be made in only one place, reducing errors and saving time.

❓ Architecture

intermediate

Which design best follows DRY for shared validation logic?

You have multiple services that need to validate user input in the same way. Which architecture approach best follows DRY?

A Each service implements its own validation code separately

B Copy validation code from one service to others when needed

C Create a shared validation library used by all services

D Skip validation to avoid repeating code

💡 Hint

Think about how to reuse code without copying it.

A shared library centralizes validation logic, so updates happen once and apply everywhere, following DRY.

❓ scaling

advanced

How does DRY help when scaling a system?

When a system grows and new features are added, how does following DRY help with scaling?

A It forces rewriting all code for each new feature

B It reduces the effort to update shared logic, making scaling faster and less error-prone

C It increases code duplication, which helps isolate features

D It makes the system slower by adding extra layers

💡 Hint

Think about how shared code affects adding or changing features.

DRY reduces duplicated code, so changes to shared logic only need to be done once, easing scaling.

❓ tradeoff

advanced

What is a potential downside of applying DRY too aggressively?

Applying DRY is good, but what problem can happen if you try to share code too much?

A It always improves performance without any downside

B It causes code duplication to increase

C It makes the system impossible to test

D It can create tight coupling making changes risky and complex

💡 Hint

Think about what happens if many parts depend on the same code.

Over-sharing code can cause tight coupling, so a small change affects many parts, increasing risk.

❓ component

expert

In a microservices system, how to apply DRY for common logging?

You have many microservices that need consistent logging. Which approach best applies DRY?

A Use a centralized logging service or library shared by all microservices

B Implement logging code separately in each microservice

C Copy logging code from one microservice to others when needed

D Avoid logging to reduce code repetition

💡 Hint

Think about how to reuse logging logic without duplication across services.

A centralized logging service or shared library ensures consistent logging and avoids code duplication, following DRY.