Software Engineer interview questions & answers — India 2026

Model answer

A process is an independent program with its own memory space. A thread is a lightweight unit of execution within a process that shares the process's memory. Multiple threads within a process can run concurrently and share data, but context switching between threads is faster than between processes. In Java, threads are managed via the Thread class or Runnable interface; in Python, the GIL limits true CPU parallelism for threads.

Model answer

Binary search is O(log n) time and O(1) space. Use it on sorted arrays or sorted data structures when you need to find an element quickly. It halves the search space on each comparison. Prefer linear search for unsorted or very small arrays where sorting overhead isn't worth it.

Model answer

A HashMap uses an array of buckets. When you call put(key, value), it computes the hash of the key, maps it to a bucket index (hash % array_size), and stores the entry. Hash collisions are handled via chaining (linked list in Java 7, balanced tree in Java 8+ when chain length > 8). Retrieval is O(1) average, O(n) worst case with poor hash distribution. Load factor (default 0.75) triggers resizing.

Model answer

CAP states that a distributed system can only guarantee two of three properties simultaneously: Consistency (all nodes see the same data), Availability (every request gets a response), and Partition Tolerance (system works despite network partitions). Since partitions are unavoidable in practice, you choose between CP (consistent but may be unavailable under partition — e.g., HBase, ZooKeeper) and AP (available but eventually consistent — e.g., Cassandra, DynamoDB).

Model answer

Key components: (1) Hash function to generate a 6-8 character short code from the long URL — use base62 encoding of a counter or MD5 truncated; (2) Database to store short→long mapping — Redis for cache, PostgreSQL for persistence; (3) 301 vs 302 redirect — 301 is permanent (browser caches, reduces server load), 302 is temporary (better for analytics); (4) Scale with CDN, read replicas, and horizontal scaling of the redirect service. Address collisions with retry logic on hash generation.

Model answer

Structure your answer using STAR: Situation (describe the incident and its impact), Task (your role — were you on-call, lead, contributor?), Action (how you diagnosed — logs, metrics, distributed tracing; what you did to mitigate — rollback, feature flag, hotfix), Result (how quickly you restored service, and what post-mortem actions prevented recurrence). Recruiters want to see calmness under pressure, clear communication, and a bias toward mitigation first, root cause second.

Model answer

SQL databases (PostgreSQL, MySQL) are relational, schema-defined, ACID-compliant, and excel at complex joins and transactions. NoSQL (MongoDB, Cassandra, Redis) are schema-flexible, horizontally scalable, and optimised for specific access patterns. Choose SQL for financial transactions, complex reporting, and structured data with relationships. Choose NoSQL for high-write-throughput, flexible/evolving schemas, time-series data, or when you need horizontal scale beyond what a single SQL instance handles.

Model answer

Acknowledge both approaches have merits. Present your preference with data: performance benchmarks, maintainability trade-offs, team familiarity, and long-term cost. Use an RFC (Request for Comments) document for significant decisions. If the team disagrees after full discussion, support the majority decision and commit fully — unless the disagreement is about correctness or security, in which case escalate appropriately.