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CS Fundamentals Interview Questions — What Senior Engineers Need to Know

CS fundamentals are the foundation every other technical topic builds on. When an interviewer asks about processes vs threads, hash table internals, or stack vs heap allocation, they’re testing whether you have genuine understanding or just memorized definitions.

These 16 questions cover the core CS concepts that senior engineers are expected to know cold: concurrency primitives, data structure internals, object-oriented design, memory models, and computational complexity. Getting these right signals that your technical knowledge has real depth.

All 16 Questions

Process vs ThreadWhat is the difference between a process and a thread?Race ConditionWhat is a race condition and how do you prevent it?Deadlock — 4 Conditions, PreventionWhat are the four conditions for deadlock and how can you prevent it?Thread Safety — Is dict Thread Safe?What does thread safety mean? Is Python's dict thread-safe?HashMap InternalsHow does a hash map work internally?Hash Collision — Chaining vs Open AddressingWhat is a hash collision and how do chaining and open addressing handle it?OOP 4 PillarsWhat are the four pillars of object-oriented programming?SOLID — All 5Explain all five SOLID principles with examples.BFS & DFSExplain BFS and DFS — when would you use each?Primitive vs Reference Types / Stack vs HeapWhat is the difference between primitive and reference types? How do stack and heap relate?Mutex vs SemaphoreWhat is the difference between a mutex and a semaphore?Virtual Memory — Paging, SwapWhat is virtual memory and how do paging and swap work?Concurrency vs ParallelismWhat is the difference between concurrency and parallelism?Overriding vs OverloadingWhat is the difference between method overriding and method overloading?Context SwitchWhat is a context switch and why is it expensive?File DescriptorWhat is a file descriptor?

How to Prepare

Focus on understanding concepts deeply enough to explain them in your own words. For each topic, practice articulating the trade-offs and real-world applications — interviewers care about practical judgment, not textbook definitions.

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