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OpenStem
@openstem · Joined Jul 2026
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Quiz10 questions
What does the Singleton pattern ensure?
AA class can be subclassed only onceBA class has at most one instance and provides a global access pointCAn object can only be created by a factoryDAll methods are static
Software · L4 · Design patterns — 10 Q
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Software · L4 · Design patterns — 10 QQuiz7 questions
Why do protocols like TLS use asymmetric crypto only for the handshake, not for bulk data?
AAsymmetric ciphers can't encrypt more than a few bytes at allBAsymmetric crypto is far slower than symmetric crypto, so it's used only to establish a shared session keyCSymmetric ciphers can't be implemented in hardwareDAsymmetric crypto is actually faster and preferred for everything
Software · L4 · Applied Cryptography — 7 Q
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Software · L4 · Applied Cryptography — 7 QQuiz7 questions
Why does range-based sharding on a monotonically increasing key cause a hotspot?
ABecause range sharding requires more storage per shardBBecause all new writes land on whichever shard currently owns the highest rangeCBecause range sharding disables replicationDBecause it forces every read to scan all shards
Software · L4 · Data Partitioning & Replication — 7 Q
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Software · L4 · Data Partitioning & Replication — 7 QQuiz7 questions
What does an error budget primarily govern?
AThe monetary cost of running infrastructureBThe tradeoff between shipping risky changes and pausing to focus on reliabilityCHow many engineers are on the on-call rotationDThe salary budget for the SRE team
Software · L4 · Site Reliability Engineering — 7 Q
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Software · L4 · Site Reliability Engineering — 7 QQuiz8 questions
What is the main tradeoff of leaderless (quorum-based) replication compared to leader-based replication?
AIt removes the need for any conflict resolutionBIt favors write availability during partitions, at the cost of needing explicit conflict resolution when replicas divergeCIt guarantees linearizability automaticallyDIt eliminates the need for multiple replicas
Software · L4 · Distributed Systems Engineering
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Software · L4 · Distributed Systems EngineeringQuiz8 questions
What is the primary benefit of moving cross-cutting network concerns into a service mesh sidecar?
AApplication code gets mTLS, retries, timeouts, and traffic shaping without implementing them itselfBIt removes the need for a network entirelyCIt eliminates the need for service-to-service authenticationDIt guarantees zero latency between services
Software · L4 · Microservices Architecture & Resilience Patterns
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Software · L4 · Microservices Architecture & Resilience PatternsQuiz8 questions
Within what scope does Kafka guarantee message ordering?
AAcross the entire topic, regardless of partitionBOnly within a single partitionCOnly across the entire clusterDKafka provides no ordering guarantees at all
Software · L4 · Event Streaming & Kafka
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Software · L4 · Event Streaming & KafkaQuiz8 questions
Which observability pillar is best suited to answering 'where in a multi-service call chain did the time go?'
AMetricsBLogsCTracesDNone of them can answer this
Software · L4 · Observability: Metrics, Logs, and Traces
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Software · L4 · Observability: Metrics, Logs, and TracesQuiz3 questions
Which of the following correctly characterises the class NP?
AProblems solvable in non-deterministic polynomial time, equivalently with polynomial-time verifiable certificatesBProblems solvable in polynomial time by a deterministic Turing machineCProblems whose complements are in PDProblems requiring exponential time in the worst case
Software · L5 · Complexity Theory
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Software · L5 · Complexity TheoryQuiz3 questions
What are the three conditions under which the FLP impossibility result applies?
ASynchrony, randomisation, and majority fault toleranceBAsynchrony, determinism, and tolerance of at least one crash faultCPartial synchrony, Byzantine faults, and n > 3f processesDAsynchrony, probabilistic algorithms, and message loss
Software · L5 · Distributed Systems Theory
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Software · L5 · Distributed Systems TheoryQuiz6 questions
What guarantee does the subset construction (Rabin & Scott, 1959) provide?
AEvery NFA can be converted to an equivalent DFA, possibly with up to 2^n states for an n-state NFABEvery DFA can be converted to a smaller NFA in polynomial timeCNFAs recognise a strictly larger class of languages than DFAsDThe subset construction reduces the number of states in every case
Software · L5 · Automata Theory & Formal Languages
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Software · L5 · Automata Theory & Formal LanguagesQuiz6 questions
What distinguishes the π-calculus from CSP in terms of expressive power?
AThe π-calculus supports asynchronous shared-memory communication; CSP does notBThe π-calculus allows channel names to be communicated as data, enabling dynamic reconfiguration of communication topologyCCSP supports recursion while the π-calculus does notDThe π-calculus has no notion of internal choice
Software · L5 · Process Calculi & Concurrency Theory
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Software · L5 · Process Calculi & Concurrency TheoryQuiz6 questions
Which statement best describes the Church–Turing thesis?
AA theorem proving Turing machines can compute any functionBAn unprovable but well-supported claim that Turing machines capture every intuitively effective computational procedureCA proof that P = NPDA theorem stating all decidable languages are regular
Software · L5 · Computability Theory
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Software · L5 · Computability TheoryQuiz6 questions
Which property defines a one-way function f?
Af is hard to compute but easy to invertBf is efficiently computable, but no PPT adversary can find a preimage of f(x) for random x except with negligible probabilityCf is a bijection with an efficiently computable inverseDf is a random oracle
Software · L5 · Cryptographic Foundations
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Software · L5 · Cryptographic FoundationsQuiz6 questions
Two operations from different transactions 'conflict' when...
AThey both read the same data itemBThey belong to transactions that started at the same timeCThey access the same data item and at least one of them is a writeDThey appear in different tables of the schema
Software · L5 · Database Theory & Query Optimization
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Software · L5 · Database Theory & Query OptimizationQuiz6 questions
Which statement correctly distinguishes data parallelism from model parallelism?
AData parallelism partitions the model across devices; model parallelism replicates itBData parallelism replicates the full model and shards the data across workers; model parallelism partitions the model itself because it does not fit on one deviceCThe two terms are synonyms for the same techniqueDData parallelism requires a parameter server; model parallelism never does
Software · L5 · Distributed Machine Learning Systems
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Software · L5 · Distributed Machine Learning SystemsQuiz6 questions
What is the key structural difference between small-step and big-step operational semantics?
ASmall-step is used only for typed languages; big-step only for untyped languagesBSmall-step defines a single-step relation e → e' composed via →*; big-step defines a direct relation e ⇓ v to the final valueCBig-step semantics can express non-termination directly, small-step cannotDThey differ only in notation and are otherwise formally identical
Software · L5 · Programming Language Semantics
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Software · L5 · Programming Language SemanticsQuiz7 questions
In a 'may' dataflow analysis, how are facts from multiple incoming CFG edges combined at a merge point?
ABy intersection (∩), keeping only facts true on every incoming pathBBy union (∪), keeping facts true on at least one incoming pathCBy discarding all incoming facts and restarting from bottomDBy averaging numeric fact values
Software · L5 · Program Analysis & Abstract Interpretation
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Software · L5 · Program Analysis & Abstract InterpretationQuiz8 questions
What does the Hoare triple {P} C {Q} assert about a program C that never terminates from some P-satisfying state?
AThe triple is falseBThe triple is vacuously true, since partial correctness only constrains terminating executionsCThe triple is undefinedDQ must be false
Software · L5 · Hoare Logic & Program Verification
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Software · L5 · Hoare Logic & Program VerificationQuiz8 questions
What is the essential structural difference between LL(1) and LR(1) parsing?
ALL(1) builds top-down by prediction; LR(1) builds bottom-up by shift and reduceBLL(1) requires more memory than LR(1) in every caseCLR(1) cannot handle any form of arithmetic expressionDThey are two names for the same algorithm
Software · L5 · Compiler Construction Theory
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Software · L5 · Compiler Construction TheoryNote~82 words · 1 min
What Is a Pattern? A pattern is something that repeats in the same way. You can find patterns everywhere! Computers use patterns too. When a program does the same thing over and over, it follows a pattern. Spotting patterns helps you solve
Software · L1 · Patterns: Spotting What Repeats
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Software · L1 · Patterns: Spotting What RepeatsNote~154 words · 1 min
Transform, Don't Mutate JavaScript arrays ship two families of methods: ones that return a new array (map, filter, slice) and ones that mutate in place (push, splice, sort). Reaching for the non-mutating family by default keeps data flow pr
Software · L1 · JavaScript: Array Method Choices
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Software · L1 · JavaScript: Array Method ChoicesNote~156 words · 1 min
Narrowing Before You Use a Value Once a value's type includes `null` or `undefined`, TypeScript won't let you use it until you've ruled those out. The two most common tools for that are the nullish coalescing operator `??` (supply a default
Software · L1 · TypeScript: Handling Optional and Nullish Values
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Software · L1 · TypeScript: Handling Optional and Nullish ValuesNote~140 words · 1 min
Four Built-ins, Four Jobs Python's built-in collections overlap in what they can hold but differ sharply in what they guarantee. Picking the wrong one doesn't usually cause a crash — it just makes the code fight against behavior it doesn't
Software · L1 · Python: Choosing the Right Collection
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Software · L1 · Python: Choosing the Right CollectionNote~97 words · 1 min
Trigger, Render, Commit A re-render doesn't touch the screen right away. React first runs your component functions to build a new tree (the render phase), then compares it against the previous tree, and only afterwards mutates the real DOM
Software · L1 · React: The Render Cycle
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Software · L1 · React: The Render CycleNote~177 words · 1 min
Reading Big-O at a Glance Big-O describes how an algorithm's work grows as the input size n grows. Knowing the common classes by name makes it fast to reason about a new problem without re-deriving the math each time. Deciding How to Solve
Software · L1 · Data Structures & Algos: Picking the Right Approach
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Software · L1 · Data Structures & Algos: Picking the Right ApproachNote~167 words · 1 min
From main() to a Running App Calling `SpringApplication.run(App.class, args)` bootstraps the whole application: it creates the ApplicationContext, loads and registers beans, applies autoconfiguration, and (for a web app) starts the embedded
Software · L1 · Spring Boot: Application Lifecycle & Logging
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Software · L1 · Spring Boot: Application Lifecycle & LoggingNote~135 words · 1 min
Match the Data Shape to the Database There is no single 'best' database — each type trades away something (joins, flexibility, raw speed) to excel at a particular access pattern. Picking well starts with describing the shape of the data and
Software · L1 · System Design: Choosing a Database Type
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Software · L1 · System Design: Choosing a Database TypeNote~141 words · 1 min
What Is a Transaction? A transaction wraps one or more statements so they succeed or fail together. `BEGIN` starts it, `COMMIT` makes every change permanent, and `ROLLBACK` undoes everything as if none of it happened. This matters whenever
Software · L1 · SQL: Transactions & ACID
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Software · L1 · SQL: Transactions & ACIDNote~109 words · 1 min
One Branch per Change Instead of committing directly to main, most teams isolate each change on its own short-lived branch. That keeps main always deployable and gives reviewers a clean diff to look at. If review comes back with requested c
Software · L1 · Git & Dev Workflow: The Feature Branch Workflow
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Software · L1 · Git & Dev Workflow: The Feature Branch Workflow