Software Engineer Interview Kit

Question 1: Walk me through how you would design a URL shortening service like bit.ly. What are the key components and considerations?

What to Look For

• • Mentions database design (storing URLs and shortened codes)
• • Discusses unique ID generation strategies
• • Considers scalability and caching
• • Addresses analytics and tracking
• • Mentions rate limiting and security
• • Discusses custom URLs and expiration

Red Flags

• • Jumps to implementation without understanding requirements
• • Ignores scalability concerns
• • No mention of database indexing
• • Doesn't consider edge cases (duplicate URLs, invalid URLs)
• • Over-engineers the solution unnecessarily

Follow-up Questions

• • How would you handle custom aliases?
• • What if we need to support 100M URLs per day?
• • How would you prevent abuse?
• • What analytics would you track?

Question 2: Explain the difference between a process and a thread. When would you use one over the other?

What to Look For

• • Process: independent memory space, more overhead
• • Thread: shared memory space, lighter weight
• • Mentions context switching costs
• • Discusses inter-process communication
• • Real-world examples of when to use each

Red Flags

• • Confuses the two concepts
• • Can't provide practical examples
• • No understanding of trade-offs
• • Incorrect technical details

Follow-up Questions

• • What is a race condition?
• • How do you handle thread synchronization?
• • What's the difference between concurrency and parallelism?

Question 3: You have a slow database query in production. Walk me through how you would diagnose and fix it.

What to Look For

• • Starts with identifying the slow query (logs, monitoring)
• • Uses EXPLAIN or query plan analysis
• • Checks for missing indexes
• • Considers query optimization (avoiding N+1, reducing joins)
• • Mentions caching strategies
• • Discusses monitoring and prevention

Red Flags

• • Immediately suggests adding indexes without analysis
• • No systematic approach to debugging
• • Doesn't mention query plans
• • No consideration of impact on production

Follow-up Questions

• • How do you identify slow queries in the first place?
• • What's the impact of adding an index on write performance?
• • When would you denormalize data?

Question 4: Write a function to reverse a linked list. Then modify it to reverse every k nodes.

What to Look For

• • Clean, readable code
• • Handles edge cases (empty list, single node, k > list length)
• • Correct pointer manipulation
• • Discusses time and space complexity
• • Tests their solution with examples

Red Flags

• • Can't handle basic linked list operations
• • Doesn't test edge cases
• • Overly complex solution
• • Can't analyze complexity

Follow-up Questions

• • What's the time and space complexity?
• • How would you test this function?
• • Can you do it recursively?
• • What if k is very large?

Question 5: How does HTTPS work? Explain the handshake process.

What to Look For

• • Mentions SSL/TLS
• • Understands certificate verification
• • Explains public/private key cryptography basics
• • Describes the handshake steps
• • Mentions symmetric vs asymmetric encryption

Red Flags

• • Confuses HTTPS with HTTP
• • No understanding of certificates
• • Can't explain why HTTPS is secure
• • Major technical inaccuracies

Follow-up Questions

• • What's a man-in-the-middle attack?
• • How do certificate authorities work?
• • What's the difference between SSL and TLS?
• • Why do we use both asymmetric and symmetric encryption?