Pricing strategy (discounts, coupons) in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Discount Application Order

In a pricing system, a customer can apply a 10% discount coupon and a $5 fixed discount coupon. Which order of applying these discounts results in the lowest final price?

A Apply only the higher discount, ignoring the other

B Apply both discounts simultaneously by adding their values

C Apply the 10% discount first, then subtract $5

D Subtract $5 first, then apply the 10% discount

💡 Hint

Think about how percentage discounts affect the price after fixed discounts.

Applying the 10% discount first reduces the base price, then subtracting $5 results in a lower final price than the reverse order.

❓ Architecture

intermediate

Designing Coupon Validation Component

Which component design best supports validating multiple coupon types (percentage, fixed amount, buy-one-get-one) in a scalable pricing system?

A A single monolithic validator that checks all coupon rules in one place

B Separate validator classes for each coupon type implementing a common interface

C Hardcoded if-else statements inside the pricing engine for each coupon type

D Validate coupons only on the client side before sending to server

💡 Hint

Consider maintainability and adding new coupon types in the future.

Using separate validator classes with a common interface allows easy extension and testing of each coupon type independently.

❓ scaling

advanced

Scaling Coupon Redemption System

Your e-commerce platform expects a sudden surge of 1 million coupon redemptions in one hour during a sale. Which approach best ensures system reliability and prevents coupon overuse?

A Implement distributed counters with eventual consistency and retry logic

B Use a centralized database with strong locking for coupon usage counters

C Allow unlimited coupon redemptions and reconcile usage offline later

D Disable coupons during high traffic to avoid race conditions

💡 Hint

Think about balancing consistency and performance under high load.

Distributed counters with eventual consistency and retries allow high throughput while minimizing contention, preventing overuse without blocking requests.

❓ tradeoff

advanced

Tradeoff Between Coupon Expiry Checks

Should coupon expiry be checked at coupon issuance or at order checkout? What is the main tradeoff?

A Check at checkout to ensure validity but increase checkout latency

B Check both at issuance and checkout to double confirm validity without tradeoffs

C Check at issuance to reduce checkout latency but risk expired coupons being issued

D Never check expiry to simplify system design

💡 Hint

Consider user experience and system performance impacts.

Checking expiry at checkout ensures coupons are valid when used but may add latency; checking only at issuance risks expired coupons being accepted later.

❓ estimation

expert

Estimating Storage for Coupon Usage Logs

Your system logs every coupon redemption with user ID, coupon ID, timestamp, and order ID. Estimate the storage needed per day if you expect 500,000 redemptions daily. Assume each log entry is 200 bytes.

A Approximately 100 MB per day

B Approximately 100 GB per day

C Approximately 10 GB per day

D Approximately 1 GB per day

💡 Hint

Multiply number of entries by size per entry and convert bytes to GB.

500,000 entries * 200 bytes = 100,000,000 bytes ≈ 100 MB per day.