Software Engineer Interview Questions (Practice with AI Feedback)

"A process is an instance of a running application that has its own isolated memory address space. A thread is the smallest execution unit within a process, sharing the parent process's memory, files, and resources. I would use multi-threading to achieve concurrency when executing independent tasks that share data, such as handling concurrent HTTP requests in a web server or processing image rendering pieces in parallel, to maximize CPU utilization without the heavy overhead of context-switching between separate processes."

"To design a URL shortener, I would set up a REST API with a POST endpoint that accepts long URLs and returns a short URL, and a GET endpoint that handles redirection. The core database would store a mapping of short keys to long URLs. To generate keys, I would use base62 encoding (a-z, A-Z, 0-9) of a sequential auto-incrementing ID generated by a distributed counter service to prevent hash collisions. redirectional requests would use HTTP 301 (Permanent Redirect) to leverage browser caching for active links, and I would use a Redis cache to keep the top 10% most frequently accessed URLs in memory."

"Searching in a balanced binary search tree takes O(log N) time in both the average and worst cases because the tree height is kept logarithmic with respect to the node count. In contrast, a hash table provides O(1) constant search time on average. However, the worst-case time complexity of a hash table search is O(N) if many keys map to the same bucket, leading to severe hash collisions where lookup requires traversing a linked list or chain of elements."

"For zero-downtime database migrations, I follow the expand-contract pattern. Instead of modifying or renaming an active column directly, I first add a new column and update the application code to write to both columns while reading from the old one. Next, I run a background script to migrate existing data in small batches. Once historical data is synced, I deploy a code update that reads from the new column. Finally, after validating stability, I deploy a cleanup migration to drop the old column."

"I follow a balanced testing pyramid. Unit tests form the base, checking individual functions or components in isolation using mock dependencies to ensure speed and fast feedback. Integration tests sit in the middle, verifying that components communicate correctly with each other or external services like database wrappers. At the top are end-to-end tests, which run the built application in a production-like environment to check complete workflows from the user's perspective."

"In my last role, our server CPU utilization spiked to 100% and crashed the application during peak traffic (Situation). I was tasked with finding the root cause and implementing a fix under tight deadlines (Task). I used APM profiling tools to inspect threads, analyzed heap dumps, and discovered a memory leak caused by a database connection client not releasing connection sockets during recursive queries (Action). I corrected the client release hooks, added an automated check to restrict connection leaks, and successfully deployed the fix (Result). CPU usage stabilized at 25% even under peak load."