Balance calculation algorithm in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding balance calculation in ledger systems

In a ledger system, the balance of an account is calculated by summing all credits and debits. Which of the following best describes the correct approach to calculate the balance?

A Sum all debit transactions and subtract all credit transactions for the account.

B Only consider the latest transaction amount as the balance.

C Sum all transactions regardless of type to get the balance.

D Sum all credit transactions and subtract all debit transactions for the account.

💡 Hint

Think about how credits and debits affect the account balance.

Credits increase the balance, debits decrease it. So, summing credits and subtracting debits gives the correct balance.

❓ Architecture

intermediate

Designing a scalable balance calculation service

You need to design a service that calculates user balances in real-time for millions of users. Which architectural choice best supports scalability and low latency?

A Precompute balances periodically and cache them in a distributed cache system.

B Use a centralized database to calculate balances on every request.

C Calculate balances by scanning all transactions on every request.

D Store balances only on user devices and sync occasionally.

💡 Hint

Consider how to reduce computation and improve response time.

Precomputing balances and caching reduces load and latency, making the system scalable.

❓ scaling

advanced

Handling concurrent balance updates

In a system where multiple transactions update the same account balance concurrently, what is the best approach to ensure balance consistency?

A Lock the entire database during balance updates to prevent conflicts.

B Allow all updates without synchronization and resolve conflicts later.

C Use optimistic concurrency control with version checks before updating balances.

D Ignore concurrency issues as they are rare and do not affect balances.

💡 Hint

Think about how to detect and handle conflicting updates efficiently.

Optimistic concurrency control allows concurrent updates but checks versions to avoid conflicts, ensuring consistency without heavy locking.

❓ tradeoff

advanced

Tradeoffs in real-time vs batch balance calculation

Choosing between real-time and batch processing for balance calculation involves tradeoffs. Which statement correctly describes a key tradeoff?

A Real-time processing reduces latency but increases system complexity and resource usage.

B Batch processing provides instant balance updates but requires more storage.

C Real-time processing is simpler to implement than batch processing.

D Batch processing eliminates the need for data consistency checks.

💡 Hint

Consider latency, complexity, and resource consumption.

Real-time systems provide quick updates but need more resources and complex design; batch systems are simpler but have latency.

❓ estimation

expert

Estimating storage for transaction history in balance calculation

You expect 10 million users, each with 1000 transactions per year. Each transaction record is 200 bytes. Estimate the total storage needed for 3 years of transaction history.

A 60 terabytes

B 6 terabytes

C 600 gigabytes

D 600 terabytes

💡 Hint

Calculate total transactions and multiply by record size, then convert to terabytes.

Total transactions = 10M users * 1000 transactions/year * 3 years = 30 billion transactions.
Storage = 30B * 200 bytes = 6 trillion bytes = 6 terabytes.