Top Software Engineer Interview Questions & Answers

O(log n). Binary search halves the search space with each comparison, making it highly efficient for sorted arrays or search spaces.

Use a hash map when you need O(1) average-case lookups by key. Use an array when you need O(1) index-based access or when ordering matters and keys are sequential integers.

Recursion is when a function calls itself to solve a smaller subproblem. Avoid it when the call stack could overflow (deep recursion without tail call optimization), or when iterative solutions are equally readable but more memory-efficient.

A stack is LIFO (last in, first out) — like a stack of plates. A queue is FIFO (first in, first out) — like a line. Use stacks for function call management, DFS, and undo operations. Use queues for BFS, task scheduling, and event processing.

Use Floyd's Cycle Detection Algorithm (tortoise and hare): two pointers move at different speeds. If they meet, there's a cycle. Time complexity O(n), space complexity O(1).

Key components: (1) API server to accept long URLs and return short ones; (2) hash function or auto-increment ID to generate short codes; (3) key-value store (Redis or DynamoDB) mapping short codes to URLs; (4) CDN for redirect performance; (5) analytics service for click tracking. Consider collision handling, expiration, and custom aliases.

Use stateless services (move state to external stores), load balancers to distribute traffic, database read replicas, caching layers (Redis/Memcached), message queues to decouple services, and CDNs for static assets. Design services that can run as multiple identical instances behind a load balancer.

In a distributed system, you can only guarantee 2 of 3: Consistency (all nodes see the same data), Availability (every request gets a response), and Partition Tolerance (system works despite network partitions). Since network partitions happen, systems must choose between CP (consistent, e.g., HBase) and AP (available, e.g., Cassandra).

Cache at multiple layers: CDN for static assets, application-level cache (Redis) for expensive queries and session data, database query cache for repeated queries. Key decisions: cache invalidation strategy (TTL, write-through, write-behind), cache warming, and what NOT to cache (user-specific, highly dynamic data).

SQL databases are relational, use structured schemas, support complex queries and ACID transactions. NoSQL databases are schema-flexible, horizontally scalable, and optimized for specific data models (document, key-value, graph, column). Use SQL for complex relationships and transactional data; NoSQL for high-scale, flexible-schema, or specific data patterns.

Use the STAR format: Situation (what the deadline was and why it mattered), Task (your responsibility), Action (how you prioritized, cut scope, or rallied the team), Result (what you shipped and what you learned). Quantify the timeline and outcome.

Show that you can advocate for your position with data and reasoning, listen to the other perspective genuinely, and ultimately commit to the team's decision without passive resistance. Interviewers want engineers who are opinionated but collaborative, not combative.

Frame it as a trade-off management problem, not a binary choice. Describe how you identify high-impact debt (what's slowing the team or causing incidents), advocate for dedicated refactoring time, track it in the backlog, and negotiate with product for capacity. Avoid making it sound like debt is always bad — strategic debt is sometimes correct.

Walk through your incident response process: detection (how you found out), mitigation (how you stopped the bleeding), root cause analysis, and the prevention work afterward. Show calm under pressure, clear communication, and a learning mindset.

Describe a constructive approach: focus on correctness, maintainability, and consistency over style preferences. Mention being specific in feedback, explaining the why behind suggestions, and being open to having your reviews challenged. Senior engineers use code review to spread knowledge, not just catch bugs.