Software Engineer
Interview Questions
18 essential questions across technical, system design, behavioral, and culture categories. Each includes scoring guidance and follow-up questions.
All Questions
18 questions
A stack is LIFO (last in, first out) like a stack of plates. A queue is FIFO (first in, first out) like a line at a store. Use stacks for undo operations, recursion, and parsing. Use queues for scheduling, breadth-first search, and handling requests in order.
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- How would you implement a queue using two stacks?
- What's the time complexity of operations on each?
SQL databases are relational - structured tables with defined schemas, great for complex queries and transactions. NoSQL databases are flexible - document, key-value, or graph-based, ideal for unstructured data and horizontal scaling.
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- When would you use MongoDB over PostgreSQL?
DNS lookup finds the IP address. Browser opens a TCP connection (TLS for HTTPS). Sends HTTP request. Server processes and returns response. Browser parses HTML, fetches resources, builds DOM, applies CSS, executes JavaScript, renders the page.
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- How does caching affect this?
- What's the role of CDNs?
First, analyze with EXPLAIN to understand the execution plan. Check for missing indexes on WHERE and JOIN columns. Look for N+1 queries. Consider denormalization for read-heavy data. Add caching for frequently accessed data.
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- When can indexes hurt performance?
REST uses HTTP methods semantically: GET (read), POST (create), PUT/PATCH (update), DELETE (remove). URLs represent resources (/users/123). Stateless requests. Proper status codes. Versioning for backwards compatibility.
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- What's the difference between PUT and PATCH?
Big O describes how algorithm performance scales with input size. O(1) is constant. O(n) is linear. O(log n) is logarithmic. O(n²) is quadratic. Focus on the dominant term for large inputs.
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- What's the complexity of quicksort?
Generate unique short codes (base62 encoding or random string with collision check). Store mapping in database. Redirect by looking up full URL. Scale with read replicas and caching (URLs rarely change). Consider analytics, expiration, and abuse prevention.
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- How do you handle 1 billion URLs?
Token bucket or sliding window algorithm. Track requests per user/IP in Redis with TTL. Return 429 when limit exceeded. Consider: per-endpoint limits, burst allowance, distributed counting, and graceful degradation.
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- How do you rate limit across multiple servers?
WebSockets for real-time bidirectional communication. Message queue for delivery guarantees. Database for persistence. Presence service for online status. Push notifications for offline users.
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- How do you ensure messages arrive in order?
Two approaches: Push (fan-out on write) - precompute feeds when posts are created. Pull (fan-out on read) - compute feed on request. Hybrid works best: push for most users, pull for celebrities.
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- How do you handle users with millions of followers?
Look for: Did they voice concerns respectfully? Did they gather data to support their position? Could they commit once a decision was made? Red flag if they can't give an example or blame others.
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- What was the outcome?
- Would you handle it differently now?
Look for: Structured learning approach. Resourcefulness in finding information. Practical application to cement knowledge. Self-awareness about knowledge gaps.
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- What resources do you typically use?
Look for: Ownership without excessive blame. Quick action to mitigate impact. Clear communication with stakeholders. Systemic fixes to prevent recurrence.
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- What did you do immediately after?
Look for: Framework for prioritization (impact, urgency). Communication with stakeholders about tradeoffs. Willingness to push back when necessary. Ability to delegate or ask for help.
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- Give me a specific example.
Use this to assess alignment with your actual work. No wrong answer - but mismatch predicts unhappiness. Probe for self-awareness about preferences.
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- How do you handle projects that don't excite you?
Look for: Context-dependent thinking. Understanding that 'it depends' on stakes and reversibility. Recognition that perfect is the enemy of good.
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- Give an example where you chose speed.
Look for: Balance of thoroughness and respect. Focus on important issues over nitpicks. Teaching mindset. Openness to receiving feedback.
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- What do you look for first?
Look for: Investment in others' growth. Patience and adapted approach. Specific examples of how they helped. Understanding that mentoring benefits both parties.
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- What was challenging about it?
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