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🖥 Interview Prep

CS Fundamentals

Big-O, memory, processes and threads, operating systems, networking, databases, security and OOP: the theory rounds.

📘 Learn it from scratch

Visual, hands-on lessons for every pattern in this topic. Do the lesson, then come back and the questions click.

Big-O in Plain EnglishMemory: The Stack, the Heap & ReferencesHow Numbers & Text Are StoredProcesses, Threads & Doing Things at OnceRace Conditions & How to Avoid ThemNetworking Deep Dive: DNS, TCP & HTTPSLatency Numbers & CachingInheritance vs CompositionSOLID Principles in Plain English

100 questions, most asked first

Ordered so the most useful questions for learning each pattern come first.

Any difficulty Easy Medium Hard

All patterns Complexity Processes & threads Memory Networking OOP SOLID & clean code Concurrency Operating systems Numbers & binary Security & crypto Design patterns Latency & caching Databases

#6SOLID principlesSOLID & clean codeMediumFree #7What is a deadlock?ConcurrencyMediumFree #8What is a race condition?ConcurrencyMediumFree #9How does a hash table work?ComplexityMediumFree #10What is virtual memory?Operating systemsMediumFree Unlock 48 more CS Fundamentals questions · all 1,200 questions for $39/year (about 11¢ a day)See full access #12IP addresses, subnets and private networksNetworkingMedium🔒#15Binary and two's complementNumbers & binaryMedium🔒#16How floating-point numbers workNumbers & binaryMedium🔒#18Symmetric vs asymmetric encryptionSecurity & cryptoMedium🔒#23The decorator patternDesign patternsMedium🔒#26Interfaces vs abstract classesOOPMedium🔒#27Amortized time (why list.append is O(1))ComplexityMedium🔒#29Comparing sorting algorithmsComplexityMedium🔒#31Mutex vs semaphoreConcurrencyMedium🔒#32Context switchingOperating systemsMedium🔒#33CPU scheduling algorithmsOperating systemsMedium🔒#34Paging and page faultsOperating systemsMedium🔒#36How garbage collection worksMemoryMedium🔒#37User mode, kernel mode and system callsOperating systemsMedium🔒#38File systems and inodesOperating systemsMedium🔒#39The TCP three-way handshakeNetworkingMedium🔒#42Bitwise operationsNumbers & binaryMedium🔒#43ASCII, Unicode and UTF-8Numbers & binaryMedium🔒#44EndiannessNumbers & binaryMedium🔒#46ACID vs BASEDatabasesMedium🔒#48TLS certificates and PKISecurity & cryptoMedium🔒#49HMAC and signed tokensSecurity & cryptoMedium🔒#50The OWASP Top 10Security & cryptoMedium🔒#51Big-O of common data structuresComplexityMedium🔒#53Hash collisions and good hash functionsSecurity & cryptoMedium🔒#55Adjacency list vs adjacency matrixComplexityMedium🔒#56Divide and conquer vs greedy vs dynamic programmingComplexityMedium🔒#59Tail recursionMemoryMedium🔒#61Functional programming vs OOPOOPMedium🔒#62Dependency injectionSOLID & clean codeMedium🔒#67Layered and clean architectureSOLID & clean codeMedium🔒#68Thread poolsProcesses & threadsMedium🔒#69The producer-consumer problemConcurrencyMedium🔒#71Async I/O vs threadsProcesses & threadsMedium🔒#72Inter-process communication (IPC)Processes & threadsMedium🔒#74What happens when you run a program?Operating systemsMedium🔒#75How a compiler worksNumbers & binaryMedium🔒#76What is JIT compilation?Numbers & binaryMedium🔒#77How packets find their way across the internetNetworkingMedium🔒#78NAT (network address translation)NetworkingMedium🔒#80How compression worksNumbers & binaryMedium🔒#82Integer overflow bugsNumbers & binaryMedium🔒#83What makes a hash function cryptographic?Security & cryptoMedium🔒#84Digital signaturesSecurity & cryptoMedium🔒#87Heisenbugs and flaky behaviourConcurrencyMedium🔒#89The fallacies of distributed computingNetworkingMedium🔒#96Memory safetyMemoryMedium🔒#99Explain a technical concept to a non-technical personComplexityMedium🔒