What should you focus on for a software engineer interview?

What makes these interviews different?

System design and architecture appeared in 45% of these interviews, compared with 20% across all interviews. Relational databases, REST API design, concurrency, and performance work also appeared more often than average. Mid-level questions made up the largest share, with junior and senior questions also included.

Start with concrete checks: can you explain when to use a database index? Can you explain how processes and threads differ, and when to choose each? For microservices, can you explain when separate deployments and team ownership justify the extra work of running services and handling communication between them?

Which common answers need more than a definition?

The most asked question was about how you use AI in daily development and which tools you use. Reviewed answers missed the link between AI use, a specific engineering task, and time saved or a better result. Can you name the tool, describe the task, and explain what changed?

Dependency injection was another common question. Reviewed answers missed its practical benefits. Can you connect it to easier testing, less dependence between components, and easier maintenance? Check that your answer covers those benefits, not just the definition.

Can you explain what the code actually does?

Reviews found missing details in language and object-oriented programming answers. Check these points in your own answers:

  • Can you name encapsulation, abstraction, inheritance, and polymorphism? Can you also name and distinguish the SOLID principles?
  • Can you explain how a Python tuple's contents not being changeable affects data safety or performance?
  • Can you distinguish the JavaScript call stack from callback queues? Explain that queued callbacks run only when the stack is empty.
  • Can you distinguish hoisting from initialization? Explain that var starts as undefined, while let and const stay unusable until initialized.
  • Can you explain when to choose an interface for a contract across unrelated classes, or an abstract class for shared behavior and state?

Can you finish a working coding answer?

A coding task appeared in 202 of 1,028 interviews. Tasks included Two Sum, finding the second-highest salary with SQL, reversing a string, and finding the largest number in an array.

Reviewed Two Sum answers missed a working function that found the numbers adding to the target and returned their indices. Does your function return the indices, not just the matching values? Can you explain its time complexity?

Can you explain an API or database flow?

Reviewed JWT answers missed the authentication flow. Can you explain that a token is issued after login and sent with later requests?

For the N+1 query problem, reviewed answers missed the query pattern. Can you describe a query loading a list, followed by an extra query for each item to fetch related data? Make that pattern clear before discussing how to avoid it.

What Software Engineer interviews cover

System design & architecture45% of interviews
Relational databases29% of interviews
Performance optimization & profiling29% of interviews
REST API design26% of interviews
Concurrency & multithreading24% of interviews
Data structures & algorithms21% of interviews

The 20 most asked Software Engineer questions

Counted by interview, not by mention: a question asked twice in one conversation counts once.

  1. How do you use AI in your day-to-day software development, and which tools do you use?

    Asked in 39 of 1,028 interviews · last asked Oct 23 · Tooling

    Show answer

    I use GitHub Copilot for code suggestions and ChatGPT to explain unfamiliar code and explore debugging ideas. For unit tests, Copilot helps draft repetitive setup so I can focus on edge cases. I review each change, run tests, and check API documentation. I avoid sharing secrets or trusting generated code without checking it.

    • Connect each tool to a real task and explain how it helped.
    • Review generated code for correctness, security, and fit with the project.
    • Check suggested APIs against documentation and test failure cases.
    • Use approved tools and follow company rules for sharing code and data.

    What the interviewer checks: The interviewer checks whether you use AI for useful tasks while staying responsible for code quality and data safety.

    Common mistake (in 8 of 18 reviewed answers): Many answers forget that naming tools is not enough; describe a specific task and how AI saved time or improved it.

    Other ways it was asked
    • “How has AI changed software development, and what AI tools have you used in a hands-on project?”
    • “How do you use AI in your work?”
    • “How do you use AI tools in your software development workflow, and what tasks do they help with?”

  2. What is dependency injection?

    Asked in 35 of 1,028 interviews · last asked Oct 21 · Concept · Junior

    Show answer

    Dependency injection means giving a class the objects it needs instead of having it create them itself. This reduces tight coupling, makes testing easier, and helps keep changes small. I use it to separate business logic from services such as databases or email senders, usually by passing them through a constructor.

    • Dependencies come from outside the class, often through its constructor.
    • Interfaces let tests replace real services with test doubles and make implementations easier to change.
    • A dependency injection container can create and connect objects, but it is not required.
    • .NET has built-in dependency injection with transient, scoped, and singleton service lifetimes.

    What the interviewer checks: The interviewer checks whether you understand how dependency injection separates responsibilities and improves testing and maintenance.

    Common mistake (in 8 of 17 reviewed answers): Many answers forget that receiving dependencies from outside the class should lead to easier testing, looser coupling, and simpler maintenance.

    Other ways it was asked
    • “What is dependency injection, and when would you use it?”
    • “What is dependency injection in .NET?”
    • “What is dependency injection, and why is it used in application design?”

  3. What are microservices, and when would you choose them over a monolith?

    Asked in 23 of 1,028 interviews · last asked Oct 16 · Design · Senior

    Show answer

    Microservices split an application into smaller services that communicate over a network and can be deployed independently. I choose them when separate teams need clear ownership, independent releases, or different scaling needs. I prefer a monolith for a small team or simple product, unless those benefits justify the extra operational work and network failures.

    • Each service covers a business function and can be changed and deployed independently.
    • Independent scaling and team ownership can justify splitting services.
    • Network calls add delay and failure risks; data consistency across services is harder.
    • A monolith is usually simpler to build, test, deploy, and monitor.

    What the interviewer checks: The interviewer checks whether you can weigh team and product needs against the costs of distributed systems.

    Common mistake (in 3 of 8 reviewed answers): Many answers forget that independent releases and team ownership must justify the extra operational work and cross-service communication costs.

    Other ways it was asked
    • “What are microservices?”
    • “What is microservices architecture, and when would you use it?”
    • “What is a microservices architecture, and when would you use one?”

  4. How do processes and threads differ, and when would you choose one over the other?

    Asked in 22 of 1,028 interviews · last asked Oct 23 · Concept · Junior

    Show answer

    A process normally has its own memory space, while threads within a process share memory. I choose processes when I need stronger isolation between tasks. I choose threads when tasks share data or need lower overhead. Threads need careful coordination because shared data can cause race conditions.

    • Processes usually cost more to start and communicate through messages or explicitly shared memory.
    • Threads share memory but each has its own stack.
    • A crashing thread can bring down its whole process; separate processes offer better fault isolation.
    • Both can run work in parallel, but language runtime limits may affect CPU-heavy threads.

    What the interviewer checks: The interviewer checks whether you can weigh isolation, overhead, shared data, and parallel execution.

    Other ways it was asked
    • “What is the difference between a process and a thread?”
    • “When would you choose multiple processes instead of multiple threads?”
    • “What is the difference between a thread and a process?”

  5. What are the four pillars of object-oriented programming?

    Asked in 21 of 1,028 interviews · last asked Oct 22 · Concept · Junior

    Show answer

    The four pillars are encapsulation, abstraction, inheritance, and polymorphism. Object-oriented programming organizes code around objects that combine data with behavior.

    • Encapsulation keeps data and related behavior together and controls access to internal state.
    • Abstraction exposes what an object can do while hiding how it works.
    • Inheritance lets a class reuse or extend another class’s behavior.
    • Polymorphism lets different object types provide different behavior through the same interface.

    What the interviewer checks: The interviewer wants to know whether you can name and explain all four pillars.

    Common mistake (in 3 of 6 reviewed answers): Many answers forget to name all four pillars, so include encapsulation, abstraction, inheritance, and polymorphism.

    Other ways it was asked
    • “What is object-oriented programming?”
    • “What are the main principles of object-oriented programming?”
    • “What are the core principles of object-oriented programming?”

  6. What is the difference between a list and a tuple in Python?

    Asked in 20 of 1,028 interviews · last asked Oct 17 · Concept · Junior

    Show answer

    A list is mutable: you can add, remove, or replace items. A tuple is immutable: its items cannot be replaced, but mutable objects inside it can still change. Use lists for collections that change and tuples for fixed groups of values. Lists are not hashable; tuples are hashable only if all their items are hashable.

    • Both keep item order and support indexing and slicing.
    • Tuple immutability prevents accidental changes to its structure, not changes inside mutable items.
    • Only tuples with hashable items can be dictionary keys or set members.
    • Tuples typically use less memory than lists in CPython; exact costs depend on the implementation.

    What the interviewer checks: The interviewer checks whether you understand mutability, hashability, and when to choose each type.

    Common mistake (in 3 of 7 reviewed answers): Many answers forget that tuple immutability protects the structure, not mutable objects stored inside it.

    Other ways it was asked
    • “What is the difference between a list and a tuple?”
    • “In Python 3, what is the difference between a list and a tuple in terms of mutability and hashability?”
    • “In Python, what is the difference between a list and a tuple, and when would you choose one over the other?”

  7. How does the JavaScript event loop work?

    Asked in 18 of 1,028 interviews · last asked Oct 8 · Concept · Mid-level

    Show answer

    The event loop lets JavaScript run queued callbacks when the call stack is empty. The stack runs current code; queues hold callbacks waiting to run. The browser or Node.js runtime handles asynchronous work and queues callbacks when ready. Promise microtasks run before the next task, such as a timer callback.

    • Long-running synchronous code blocks other callbacks on the same thread.
    • Microtasks include Promise handlers and queueMicrotask callbacks; they drain before the next task.
    • A timer delay sets a minimum wait, not an exact execution time.
    • Node.js uses event loop phases for timers, I/O, and other callbacks; browsers organize work differently.
    JavaScript
    console.log('start');
setTimeout(() => console.log('timer'), 0);
Promise.resolve().then(() => console.log('promise'));
console.log('end');
// Output: start, end, promise, timer

    What the interviewer checks: The interviewer checks whether you can explain asynchronous execution and predict callback order.

    Common mistake (in 4 of 7 reviewed answers): Many answers forget that the call stack and callback queues are separate, and queued callbacks wait until the stack is empty.

    Other ways it was asked
    • “What is the event loop in JavaScript?”
    • “Can you explain the event loop?”
    • “What does the event loop do in Node.js?”

  8. What are database indexes, and when would you use them?

    Asked in 18 of 1,028 interviews · last asked Oct 14 · Concept · Junior

    Show answer

    A database index is a separate data structure that helps the database find rows without scanning the whole table. I use indexes on columns often used in filters, joins, or sorting. They can speed up reads, but use storage and add work to inserts, updates, and deletes.

    • Choose indexes based on common queries, not every column.
    • Indexes often help most when a query selects a small part of a large table.
    • For multi-column indexes, column order matters.
    • Check query plans to see whether an index is used and improves performance.

    What the interviewer checks: The interviewer is checking whether you can balance faster reads against storage and write costs.

    Other ways it was asked
    • “What is indexing?”
    • “What are database indexes, and what are they used for?”
    • “What are database indexes, and how do they affect database performance?”

  9. What is the difference between var, let, and const in JavaScript?

    Asked in 16 of 1,028 interviews · last asked Oct 7 · Concept · Junior

    Show answer

    `var` is scoped to a function or the top level, while `let` and `const` are block-scoped. All three are hoisted, but only `var` is initialized to `undefined` before execution. `let` allows reassignment; `const` does not. I prefer `const`, use `let` for reassignment, and avoid `var` in new code.

    • `let` and `const` are in the temporal dead zone until initialized; accessing them there throws a ReferenceError.
    • `const` prevents reassignment, but its object properties or array contents can still change.
    • `var` allows repeated declarations of the same variable; `let` and `const` do not allow same-scope redeclaration.

    What the interviewer checks: The interviewer is checking whether you understand scope, initialization, reassignment, and which declaration to choose.

    Common mistake (in 3 of 6 reviewed answers): Many answers forget that hoisting is not initialization: `let` and `const` are hoisted but remain unusable until initialized.

    Other ways it was asked
    • “What is the difference between var, let, and const?”
    • “In JavaScript, can you differentiate between let, var, and const?”
    • “What is the difference between `let`, `const`, and `var` in JavaScript?”

  10. Write a function that solves the Two Sum problem. What is the time complexity of your solution?

    Asked in 16 of 1,028 interviews · last asked Oct 23 · Write code · Junior

    Show answer

    I use a hash map to return the indices of two numbers that add up to the target. For each number, I check whether its needed partner appeared earlier. This takes O(n) average time and O(n) extra space. If no pair exists, I return an empty list.

    • Store each seen number and its index in a hash map.
    • Check before storing to avoid using the same index twice.
    • Duplicate values work when they appear at different indices.
    • Hash map lookups and inserts take O(1) average time.
    Python
    def two_sum(nums, target):
    seen = {}
    for i, num in enumerate(nums):
        needed = target - num
        if needed in seen:
            return [seen[needed], i]
        seen[num] = i
    return []

    What the interviewer checks: The interviewer checks whether you can write correct code, use a hash map, and explain time and space costs.

    Common mistake (in 4 of 5 reviewed answers): Many answers forget that a complete solution must return the indices, not just describe the approach.

    Other ways it was asked
    • “Write a function that solves the Two Sum problem.”
    • “What is the time complexity of your Two Sum solution?”
    • “What is the time complexity of a solution to the Two Sum problem?”

  11. Can you explain the SOLID principles?

    Asked in 16 of 1,028 interviews · last asked Oct 15 · Concept · Mid-level

    Show answer

    SOLID gives five guidelines for object-oriented design. Single Responsibility means one reason to change; Open/Closed means open for extension, closed for modification. Liskov Substitution means subtypes must honor their base type’s contract; Interface Segregation means clients should not depend on methods they do not need. Dependency Inversion means high-level policy and low-level details depend on abstractions.

    • Keep each class focused on one responsibility, not necessarily one method.
    • Extend behavior without changing stable code; subclasses must preserve expected behavior.
    • Use focused interfaces and depend on abstractions rather than concrete implementations.
    • Apply these guidelines where they help; unnecessary abstractions make code harder to understand.

    What the interviewer checks: The interviewer checks whether you understand all five principles and how they help keep code easy to change.

    Common mistake (in 5 of 6 reviewed answers): Many answers forget that all five principles have different goals, so name each one and explain its meaning.

    Other ways it was asked
    • “What are the SOLID principles?”
    • “Can you explain a bit more about what each SOLID principle means?”
    • “What are the SOLID principles? Can you name three or all five?”

  12. What is middleware, and how is it used in ASP.NET Core?

    Asked in 15 of 1,028 interviews · last asked Oct 6 · Concept · Junior

    Show answer

    Middleware is code that handles HTTP requests and responses in a pipeline. In ASP.NET Core, each component can run code before and after calling the next component, or stop the request from going further. Middleware handles tasks such as logging, error handling, authentication, and serving static files.

    • Register middleware in Program.cs using methods such as app.UseAuthentication() or app.Use().
    • Order matters: requests move forward through the pipeline, and responses return through it.
    • A component can skip the next component and return a response directly.
    • Place error-handling middleware early, and authentication before authorization.

    What the interviewer checks: The interviewer is checking whether you understand the request pipeline, middleware order, and when processing stops.

    Other ways it was asked
    • “What is middleware?”
    • “What is middleware in ASP.NET Core?”
    • “What is middleware in a web application?”

  13. What are the different SQL joins, and how do INNER, LEFT, and FULL OUTER JOIN differ?

    Asked in 15 of 1,028 interviews · last asked Oct 22 · Concept · Junior

    Show answer

    INNER JOIN returns only matching row pairs. LEFT JOIN also keeps unmatched left rows; RIGHT JOIN also keeps unmatched right rows. FULL OUTER JOIN keeps unmatched rows from both sides. Outer joins fill missing-side columns with NULL; I use them when unmatched rows must stay in the result.

    • CROSS JOIN returns every possible pair of rows from the two tables.
    • A self join joins a table to itself, usually using different aliases.
    • Multiple matches produce multiple result rows; joins do not automatically remove duplicates.
    • Database support differs: MySQL does not directly support FULL OUTER JOIN.

    What the interviewer checks: The interviewer checks whether you understand which rows each join keeps and how missing matches appear.

    Other ways it was asked
    • “What is the difference between INNER JOIN, LEFT JOIN, and FULL OUTER JOIN?”
    • “What’s the difference between an inner and outer join?”
    • “What is the difference between inner, left, and right joins?”

  14. What are method overloading and method overriding?

    Asked in 14 of 1,028 interviews · last asked Oct 22 · Concept · Junior

    Show answer

    In Java, overloading means using the same method name with different parameter lists. Overriding means a subclass provides a new implementation of an inherited instance method with the same signature and a compatible return type. Overloads are selected at compile time; overridden implementations are selected at runtime based on the actual object.

    • Overloaded methods differ in parameter count, types, or type order—not just return type.
    • An overriding method cannot reduce the inherited method's access level.
    • Static methods are hidden, not overridden. Final methods cannot be overridden.

    What the interviewer checks: The interviewer checks whether you understand method signatures, inheritance, and compile-time versus runtime method selection.

    Other ways it was asked
    • “What is method overloading?”
    • “What is the difference between method overloading and method overriding?”
    • “What is method overriding in Java?”

  15. What is JWT authentication?

    Asked in 14 of 1,028 interviews · last asked Oct 15 · Concept · Junior

    Show answer

    JWT authentication uses a JSON Web Token to carry claims about a user. After a successful login, the server issues a signed JWT, which the client sends with later requests. The server verifies its signature and checks claims, such as expiration, before accepting it, without needing a server-side session lookup.

    • Clients often send the token in the Authorization header using Bearer.
    • A valid signature detects changes and proves signing by a trusted issuer.
    • Signed JWT contents are readable, not encrypted; do not include secrets.
    • Check expiration, issuer, and audience; immediate revocation usually needs extra server-side state.

    What the interviewer checks: The interviewer checks whether you understand the login flow, token verification, and security limits of JWTs.

    Common mistake (in 3 of 8 reviewed answers): Many answers forget that the server issues the JWT after login and the client sends it with later requests.

    Other ways it was asked
    • “What is JWT?”
    • “What is a JWT, and how does it work?”
    • “What is JWT-based authentication?”

  16. What is the difference between an interface and an abstract class?

    Asked in 13 of 1,028 interviews · last asked Oct 21 · Concept · Junior

    Show answer

    An interface defines a contract that classes can follow. An abstract class provides a shared base with common code and instance state. I use an interface for a shared role across unrelated classes, and an abstract class when related classes need shared state or behavior.

    • In Java, a class can implement multiple interfaces but extend only one class.
    • Interface features vary by language; modern Java interfaces can include default method implementations.
    • Java abstract classes can have constructors and instance fields, but cannot be instantiated directly.

    What the interviewer checks: The interviewer checks whether you understand both concepts and can choose between them in practice.

    Common mistake (in 3 of 5 reviewed answers): Many answers forget that the choice depends on needing a shared contract versus shared behavior and state.

    Other ways it was asked
    • “What is the difference between an abstract class and an interface?”
    • “What is the difference between an abstract class and an interface, and why would you use an abstract class instead of an interface?”
    • “What is the difference between abstraction and an interface?”

  17. What is polymorphism, and how does it work in Java?

    Asked in 13 of 1,028 interviews · last asked Oct 17 · Concept · Junior

    Show answer

    Polymorphism lets the same interface or parent type represent objects with different behavior. In Java, an overridden instance method runs based on the object's actual class, even through a parent or interface reference. Method overloading is different: Java chooses the method signature at compile time based on the declared types of the arguments.

    • An interface or parent reference can hold an object of a compatible child class.
    • Overriding provides runtime polymorphism; overloading is resolved at compile time.
    • Static methods are hidden, not overridden.
    Code
    interface Animal { void speak(); }
class Dog implements Animal {
    public void speak() { System.out.println("Woof"); }
}
public class Demo {
    public static void main(String[] args) {
        Animal animal = new Dog();
        animal.speak(); // Calls Dog.speak()
    }
}

    What the interviewer checks: The interviewer checks whether you understand shared types, runtime method selection, and the difference between overriding and overloading.

    Other ways it was asked
    • “What is polymorphism?”
    • “What is polymorphism in Java?”
    • “Can you tell me what polymorphism is?”

  18. What is the difference between the HTTP PUT and PATCH methods?

    Asked in 13 of 1,028 interviews · last asked Oct 23 · Concept · Junior

    Show answer

    PUT replaces a resource's state with the supplied representation. PATCH applies changes without replacing the whole resource. PUT is idempotent, so repeating the same request has the same intended effect as sending it once. PATCH may be idempotent, depending on the changes it applies.

    • Use PUT for a full replacement and PATCH for partial changes.
    • PUT can also create a resource at the requested URL if the server allows it.
    • Setting a field to a fixed value can be idempotent; incrementing it usually is not.
    • The PATCH document format defines how changes are applied.

    What the interviewer checks: The interviewer checks whether you understand replacement, partial updates, and the effect of repeating requests.

    Other ways it was asked
    • “What is the difference between PUT and PATCH?”
    • “What is the difference between the PUT and PATCH methods?”
    • “What is the difference between the PUT and PATCH HTTP methods?”

  19. What is the N+1 query problem, and how can you avoid it?

    Asked in 13 of 1,028 interviews · last asked Oct 15 · Concept · Mid-level

    Show answer

    The N+1 query problem happens when one query loads a list, then one extra query per item loads related data. It often comes from lazy loading in an ORM and causes many database round trips. I avoid it by loading related data upfront with joins or batched queries, then check the query logs.

    • For N items, the pattern runs N+1 queries instead of a small fixed number.
    • Eager loading can use joins or separate batched queries, depending on the ORM.
    • Joins can repeat parent data; batching can avoid that duplication.
    • Check query counts as the list grows, not just with one item.

    What the interviewer checks: The interviewer is checking whether you can spot repeated database calls and choose a better way to load related data.

    Common mistake (in 3 of 7 reviewed answers): Many answers forget that the pattern starts with one list query, followed by one related-data query per item.

    Other ways it was asked
    • “What is the N+1 query problem, and how do you fix it?”
    • “What is the N+1 query problem?”
    • “How can you avoid the N+1 query problem?”

  20. What is React, and why is it used?

    Asked in 12 of 1,028 interviews · last asked Sep 13 · Concept · Junior

    Show answer

    React is a JavaScript library for building user interfaces from reusable components. It updates the screen when data changes, so I can describe what to show instead of changing the page by hand. It helps keep interactive applications organized and easier to maintain.

    • Components let you reuse interface code across an application.
    • Props pass data into components; state tracks data that can change.
    • React handles rendering, but routing and other application features often need additional tools.

    What the interviewer checks: The interviewer is checking whether you understand React’s purpose, component model, and main benefits.

    Other ways it was asked
    • “What is React?”
    • “What is React, and what is it used for?”
    • “What is React, and what does it do?”

Programming languages and concurrency interview questions

Language questions cover types, collections, runtimes, memory management, exceptions, asynchronous code, and threads. 1,037 questions.

  1. In JavaScript, what is the difference between == and ===, and when would you choose one over the other?

    Asked in 11 of 1,028 interviews · last asked Sep 17 · Concept · Junior

    Other ways it was asked
    • “What is the difference between == and === in JavaScript?”
    • “What is the difference between `==` and `===` in JavaScript?”
    • “When would you use ==, and when would you use ===?”

  2. How do async and await work in C#, and when would you use them?

    Asked in 10 of 1,028 interviews · last asked Oct 5 · Concept · Mid-level

    Other ways it was asked
    • “What are async and await in C#, and how do they support asynchronous programming?”
    • “What are async and await in C#, and why are they important?”
    • “What happens behind the scenes when you use async and await in C#—and why does it matter?”

  3. Can you explain closures in JavaScript?

    Asked in 9 of 1,028 interviews · last asked Oct 15 · Concept · Junior

    Other ways it was asked
    • “What is a closure in JavaScript?”
    • “Why are closures used in JavaScript?”
    • “What is a closure in JavaScript, and how does it work?”

  4. What is the difference between StringBuffer and StringBuilder?

    Asked in 8 of 1,028 interviews · last asked Oct 13 · Concept · Junior

    Other ways it was asked
    • “What is the difference between String, StringBuilder, and StringBuffer?”
    • “What is the difference between StringBuilder and StringBuffer?”
    • “What is one key difference between StringBuilder and StringBuffer in Java, and when would you use each?”

  5. What is Python?

    Asked in 8 of 1,028 interviews · last asked Sep 27 · Concept · Junior

    Other ways it was asked
    • “What is the definition of Python?”

  6. What is the difference between mutable and immutable objects?

    Asked in 8 of 1,028 interviews · last asked Oct 22 · Concept · Junior

    Other ways it was asked
    • “Can you explain mutable and immutable objects, with examples?”
    • “What is the difference between mutable and immutable objects in terms of memory allocation?”
    • “What are mutable and immutable objects?”

  7. Explain hoisting in JavaScript.

    Asked in 7 of 1,028 interviews · last asked Oct 21 · Concept · Junior

    Other ways it was asked
    • “What is hoisting in JavaScript?”
    • “Tell me about hoisting in JavaScript.”
    • “Can you explain hoisting in JavaScript?”

  8. How do HashMap and ConcurrentHashMap differ in thread safety, reads, and updates?

    Asked in 7 of 1,028 interviews · last asked Oct 23 · Concept · Mid-level

    Other ways it was asked
    • “How is HashMap different from ConcurrentHashMap in Java?”
    • “Can you explain the difference between HashMap and ConcurrentHashMap?”
    • “Can you explain the difference between HashMap and ConcurrentHashMap, and when would you use each?”

  9. What is Java?

    Asked in 7 of 1,028 interviews · last asked Sep 27 · Concept · Junior

  10. What string hashing algorithm is used in Python?

    Asked in 7 of 1,028 interviews · last asked Oct 20 · Concept · Mid-level

    Other ways it was asked
    • “What hashing algorithm is used for strings in Python?”

  11. What is a callback function in JavaScript?

    Asked in 7 of 1,028 interviews · last asked Sep 30 · Concept · Junior

    Other ways it was asked
    • “Can you explain what a callback function is?”
    • “What is a callback function?”
    • “What is a callback function used for in JavaScript?”

  12. What is the difference between require and import in Node.js?

    Asked in 6 of 1,028 interviews · last asked Oct 19 · Concept · Junior

    Other ways it was asked
    • “Could you clarify the syntax differences between require and import, and explain how their loading mechanisms affect module behavior in Node.js?”
    • “What is the difference between `require` and `import` in Next.js?”
    • “Can you explain how require and import differ in syntax and when each is supported in Node.js?”
Show 4 more

  1. What is the difference between IEnumerable and IQueryable in .NET?

    Asked in 6 of 1,028 interviews · last asked Oct 2 · Concept · Mid-level

    Other ways it was asked
    • “What is the difference between IQueryable and IEnumerable?”
    • “In the .NET framework, what’s the difference between IEnumerable and IQueryable, and when would you choose one over the other?”
    • “What's the difference between IEnumerable and IQueryable?”

  2. How does HashMap work internally in Java?

    Asked in 6 of 1,028 interviews · last asked Oct 16 · Concept · Senior

    Other ways it was asked
    • “How does Java's HashMap work?”
    • “How does HashMap work in Java?”
    • “How does HashMap handle internal operations in modern Java?”

  3. What's the difference between an interface and a type in TypeScript?

    Asked in 6 of 1,028 interviews · last asked Oct 7 · Concept · Mid-level

    Other ways it was asked
    • “In TypeScript, what's the difference between type and interface, and when would you prefer one over the other in a UI component code base?”
    • “In TypeScript, what's the difference between type and interface, and when do you prefer one over the other?”
    • “In TypeScript, what's the difference between type and interface? When would you choose one over the other in a React component library?”

  4. What are decorators in Python?

    Asked in 6 of 1,028 interviews · last asked Oct 15 · Concept · Junior

    Other ways it was asked
    • “When would you use Python decorators?”
    • “What is a decorator in Python?”
    • “What is a Python decorator?”

Data structures and algorithms interview questions

Coding tasks cover strings, arrays, maps, linked lists, searching, caching, and how much time and memory your solution uses. 478 questions.

  1. Write code to reverse a string.

    Asked in 6 of 1,028 interviews · last asked Sep 7 · Write code · Junior

    Other ways it was asked
    • “Write Java code to reverse a string.”
    • “How would you write code to reverse a string?”
    • “How would you reverse a string?”

  2. What is a linked list?

    Asked in 4 of 1,028 interviews · last asked Sep 13 · Concept · Junior

    Other ways it was asked
    • “Can you explain a linked list?”
    • “What is a linked list, and how does it work?”
    • “How does a linked list work?”

  3. What is a HashMap?

    Asked in 3 of 1,028 interviews · last asked May 1 · Concept · Junior

    Other ways it was asked
    • “What is a HashMap in Java?”

  4. What is a list?

    Asked in 3 of 1,028 interviews · last asked Oct 17 · Concept · Junior

    Other ways it was asked
    • “What is a list, and what types of items can it contain?”

  5. What is an array?

    Asked in 3 of 1,028 interviews · last asked Oct 22 · Concept · Junior

    Other ways it was asked
    • “Define an array.”
    • “What is an array in JavaScript?”

  6. Write code to find the largest number in an array.

    Asked in 3 of 1,028 interviews · last asked Oct 22 · Write code · Junior

    Other ways it was asked
    • “Write a simple function to find the largest number in an array of numbers.”
    • “Write code to find the maximum number in an array in O(n) time.”

  7. Write code for the Two Sum problem.

    Asked in 2 of 1,028 interviews · last asked Oct 19 · Write code · Junior

    Other ways it was asked
    • “Can you write the code for the Two Sum problem?”
    • “Can you write the solution for Two Sum?”
    • “How would you solve the Two Sum coding question?”

  8. Find the longest substring without repeated characters.

    Asked in 2 of 1,028 interviews · last asked Oct 5 · Write code · Junior

    Other ways it was asked
    • “Given a string, find the length of the longest substring without repeating characters.”
    • “How can you find the length of the longest substring without repeating characters without repeatedly scanning the substring?”

  9. What is the difference between an array and a list?

    Asked in 2 of 1,028 interviews · last asked Sep 27 · Concept · Junior

  10. What is Dijkstra's algorithm, and when is it used?

    Asked in 2 of 1,028 interviews · last asked Oct 9 · Concept · Junior

    Other ways it was asked
    • “What is the Dijkstra algorithm?”

  11. What is the time complexity of merge sort and quicksort?

    Asked in 2 of 1,028 interviews · last asked Oct 9 · Concept · Junior

    Other ways it was asked
    • “What are the time complexities of bubble sort and merge sort?”
    • “What is the time complexity of merge sort?”

  12. Given existing conference room bookings as an array of start- and end-time pairs and a new meeting request in the same format, write a function that determines whether the new meeting can be booked without overlapping any existing meeting.

    Asked in 2 of 1,028 interviews · last asked Jun 23 · Write code · Junior

    Other ways it was asked
    • “Given a list of existing conference-room bookings, each represented by a start time and an end time, and one new meeting request in the same format, write a function that returns true if the new meeting can be booked without overlapping any existing meeting, and false otherwise. Assume one meeting ending exactly when another starts is allowed.”
Show 7 more

  1. Why would you choose breadth-first search (BFS) over depth-first search (DFS)?

    Asked in 2 of 1,028 interviews · last asked Sep 4 · Concept · Mid-level

    Other ways it was asked
    • “What is the difference between depth-first search (DFS) and breadth-first search (BFS)?”

  2. How would you design and implement an LRU cache?

    Asked in 2 of 1,028 interviews · last asked Jul 27 · Write code · Mid-level

  3. Write a function that prints “even” if a number x is even, or “odd” otherwise.

    Asked in 2 of 1,028 interviews · last asked Aug 21 · Write code · Junior

    Other ways it was asked
    • “Write a program that prints "even" if a number x is even, otherwise prints "odd".”

  4. What is the three-sum problem, and how would you solve it?

    Asked in 2 of 1,028 interviews · last asked Sep 5 · Write code · Junior

    Other ways it was asked
    • “How would you implement a solution to the three-sum problem?”
    • “What is the 3Sum problem?”

  5. Design an LRU cache with get(key) and put(key, value) operations that run in O(1) time.

    Asked in 2 of 1,028 interviews · last asked Sep 10 · Write code · Junior

    Other ways it was asked
    • “Design and implement an LRU cache with get(key) and put(key, value) operations.”

  6. Design a function that takes a list of integers and returns the length of the longest consecutive sequence in the list.

    Asked in 2 of 1,028 interviews · last asked Sep 18 · Write code · Mid-level

    Other ways it was asked
    • “Given an array of integers, find the length of the longest consecutive sequence.”

  7. Write code to check whether parentheses are valid.

    Asked in 2 of 1,028 interviews · last asked Oct 20 · Write code · Junior

    Other ways it was asked
    • “What test cases would you write to ensure a function that checks whether parentheses are valid, including nested parentheses, is correct and robust?”
    • “How would you structure a function that checks whether parentheses are valid, and what should it do when it encounters a closing bracket that does not match the expected type?”

All Data Structures and Algorithms interview questions

Object-oriented programming and design patterns interview questions

Object-oriented questions focus on core concepts, SOLID principles, dependency injection, design patterns, and code that is easier to maintain. 376 questions.

  1. In ASP.NET Core, what's the difference between transient, scoped, and singleton lifetimes?

    Asked in 9 of 1,028 interviews · last asked Sep 18 · Concept · Mid-level

    Other ways it was asked
    • “Can you explain the differences between transient, scoped, and singleton service lifetimes in ASP.NET Core, and give a concrete example of when you would use each?”
    • “Explain transient, scoped, and singleton lifetimes in ASP.NET Core.”
    • “In ASP.NET Core, how do you decide between singleton, scoped, and transient? What is a real example of a bug caused by choosing the wrong lifetime?”

  2. What is inheritance, and which types of inheritance does Java support?

    Asked in 9 of 1,028 interviews · last asked Sep 27 · Concept · Junior

    Other ways it was asked
    • “What is inheritance?”
    • “Which types of inheritance does Java support?”
    • “What is the concept of inheritance?”

  3. Which design patterns have you used, and when would you use them?

    Asked in 8 of 1,028 interviews · last asked Oct 14 · Concept · Mid-level

    Other ways it was asked
    • “Which design patterns do you know, and when do you apply them?”
    • “Which design patterns are you familiar with?”
    • “What do you know about design patterns?”

  4. What is abstraction?

    Asked in 7 of 1,028 interviews · last asked Sep 22 · Concept · Junior

    Other ways it was asked
    • “What do you mean by abstraction?”

  5. What is the MVC architecture?

    Asked in 7 of 1,028 interviews · last asked Oct 22 · Concept · Junior

    Other ways it was asked
    • “What is MVC?”
    • “At a basic level, what is MVC?”
    • “Explain MVC.”

  6. What are the different types of bean scopes in Spring?

    Asked in 6 of 1,028 interviews · last asked Sep 28 · Concept · Mid-level

    Other ways it was asked
    • “What different scopes can a Spring bean have?”
    • “What scopes are available for Spring beans, and what does each scope mean?”
    • “What bean scopes are available in Spring?”

  7. How would you design an immutable class in Java?

    Asked in 5 of 1,028 interviews · last asked Oct 6 · Concept · Mid-level

    Other ways it was asked
    • “How do you make a class immutable in Java?”
    • “Can you explain immutable class design?”
    • “What does immutable class design mean in Java?”

  8. What is an interface in Java?

    Asked in 5 of 1,028 interviews · last asked Sep 30 · Concept · Junior

    Other ways it was asked
    • “What is an interface in Java, and what is it used for?”
    • “What advantages do interfaces provide in Java?”

  9. What are the types of dependency injection in Spring?

    Asked in 5 of 1,028 interviews · last asked Oct 16 · Concept · Junior

    Other ways it was asked
    • “What types of dependency injection does Spring support, which type is recommended, and why?”
    • “What are the types of dependency injection?”
    • “What are the different ways of dependency injection in Spring?”

  10. What is inversion of control?

    Asked in 5 of 1,028 interviews · last asked Oct 7 · Concept · Junior

    Other ways it was asked
    • “What is inversion of control (IoC)?”
    • “What does inversion of control mean in a Spring application?”
    • “What is inversion of control in Spring Boot?”

  11. Can you explain how Java handles multiple inheritance?

    Asked in 4 of 1,028 interviews · last asked Oct 8 · Concept · Junior

    Other ways it was asked
    • “How can you implement multiple inheritance in Java?”
    • “How can you achieve multiple inheritance in Java when classes do not support it?”
    • “Why does Java not allow multiple inheritance?”

  12. What is domain-driven design, and when would you use it?

    Asked in 3 of 1,028 interviews · last asked Sep 28 · Concept · Senior

    Other ways it was asked
    • “What is domain-driven design (DDD)?”
    • “What is domain-driven design used for, what are its advantages and disadvantages, and where did it originate?”
    • “What is domain-driven design (DDD), and in what situations is it particularly useful?”
Show 2 more

  1. Can a static method be overridden?

    Asked in 3 of 1,028 interviews · last asked Sep 9 · Concept · Junior

    Other ways it was asked
    • “Can you override a static method in Java?”
    • “Why can't static methods be overridden in Java?”

  2. What is OOP, and can you define it?

    Asked in 3 of 1,028 interviews · last asked Oct 22 · Concept · Junior

    Other ways it was asked
    • “What is OOP?”

Frontend and mobile development interview questions

Frontend and mobile questions cover HTML, CSS, browsers, tools, React, Angular, Next.js, state management, rendering, and mobile interfaces. 1,048 questions.

  1. What is useEffect in React?

    Asked in 10 of 1,028 interviews · last asked Oct 2 · Concept · Junior

    Other ways it was asked
    • “What is the useEffect hook in React, and when would you use it?”
    • “What is React's useEffect hook used for?”
    • “Can you explain useEffect in React?”

  2. What is the virtual DOM in React?

    Asked in 10 of 1,028 interviews · last asked Oct 21 · Concept · Junior

    Other ways it was asked
    • “What is the Virtual DOM?”
    • “Why does React use a virtual DOM?”
    • “What are the DOM and Virtual DOM in React?”

  3. What are props and state in React, and what is the difference between them?

    Asked in 9 of 1,028 interviews · last asked Oct 15 · Concept · Junior

    Other ways it was asked
    • “What are props in React?”
    • “What is the difference between state and props?”
    • “What is the difference between props and state in React Native?”

  4. What's the difference between server-side rendering and client-side rendering in Next.js?

    Asked in 8 of 1,028 interviews · last asked Oct 2 · Concept · Mid-level

    Other ways it was asked
    • “What is the difference between server-side rendering (SSR) and client-side rendering (CSR) in Next.js?”
    • “When would you use client-side rendering rather than server-side rendering in Next.js?”
    • “What is server-side rendering in Next.js?”

  5. What is the DOM?

    Asked in 8 of 1,028 interviews · last asked Sep 7 · Concept · Junior

    Other ways it was asked
    • “What is the DOM (Document Object Model)?”
    • “What is the DOM, and what is it used for in JavaScript?”
    • “What is the DOM used for in JavaScript?”

  6. How do hooks work in React?

    Asked in 8 of 1,028 interviews · last asked Oct 8 · Concept · Junior

    Other ways it was asked
    • “What is a hook in React?”
    • “What are the hooks available in React?”
    • “How do state and Hooks work in React?”

  7. How do CSS Grid and Flexbox differ, and when would you choose each?

    Asked in 7 of 1,028 interviews · last asked Oct 7 · Concept · Junior

    Other ways it was asked
    • “What is the difference between Flexbox and CSS Grid?”
    • “What is the difference between Flexbox and Grid?”
    • “What is the difference between CSS Flexbox and CSS Grid?”

  8. What is Redux?

    Asked in 7 of 1,028 interviews · last asked Oct 15 · Concept · Junior

    Other ways it was asked
    • “Can you explain what Redux does?”
    • “What is Redux, and how does it help manage application state?”
    • “What is Redux, and how is it used with React?”

  9. What are Angular signals, and how are they used?

    Asked in 6 of 1,028 interviews · last asked Oct 23 · Concept · Mid-level

    Other ways it was asked
    • “What are Angular signals, and how do they work?”
    • “What are Angular Signals, and when would you use them?”
    • “Why are Angular signals used?”

  10. What is the difference between controlled and uncontrolled components in React?

    Asked in 6 of 1,028 interviews · last asked Oct 8 · Concept · Junior

    Other ways it was asked
    • “What are controlled and uncontrolled components in React, and when would you use each?”
    • “In React, can you explain the difference between a controlled and uncontrolled component, and when you choose one over the other?”
    • “Can you explain controlled and uncontrolled components in React?”

  11. What is the difference between SSG and SSR in Next.js?

    Asked in 6 of 1,028 interviews · last asked Oct 7 · Concept · Mid-level

    Other ways it was asked
    • “What is the difference between SSR and SSG in Next.js?”
    • “In Next.js, what is the practical difference between SSR and SSG in terms of caching, performance, and data freshness?”
    • “What is the difference between SSR and ISR in Next.js?”

  12. How do you choose between local state, Context, Redux, Zustand, and React Query?

    Asked in 6 of 1,028 interviews · last asked Oct 20 · Concept · Mid-level

    Other ways it was asked
    • “How do you manage component state in a React application?”
    • “What are the different ways to manage state in a React application?”
    • “What are the options for centralized state management in a React application?”
Show 7 more

  1. What is useState in React?

    Asked in 6 of 1,028 interviews · last asked Oct 16 · Concept · Junior

    Other ways it was asked
    • “What is the purpose of useState in React?”
    • “What is the useState hook in React, and when would you use it?”
    • “What is useState in React, and how do you use it?”

  2. What are components in React?

    Asked in 6 of 1,028 interviews · last asked Sep 10 · Concept · Junior

    Other ways it was asked
    • “What is a component in React?”
    • “What are the different types of components in React?”
    • “What are React components?”

  3. What are the differences between useEffect, useMemo, and useCallback?

    Asked in 5 of 1,028 interviews · last asked Sep 18 · Concept · Mid-level

    Other ways it was asked
    • “What is the difference between useMemo and useCallback?”
    • “What is the difference between useMemo and useCallback, and when would you use them?”
    • “When would you use useEffect, useMemo, and useCallback in a React application?”

  4. Can you describe the difference between useEffect and useLayoutEffect, and when you would use each?

    Asked in 5 of 1,028 interviews · last asked Oct 6 · Concept · Mid-level

    Other ways it was asked
    • “In React, what's the difference between useEffect and useLayoutEffect, and when would you choose one over the other?”
    • “What is the difference between useEffect and useLayoutEffect?”
    • “What are hooks, and what is the difference between useEffect and useLayoutEffect?”

  5. How do Angular and React differ, and how would you choose between them?

    Asked in 4 of 1,028 interviews · last asked Oct 16 · Concept · Mid-level

    Other ways it was asked
    • “What is the difference between Angular and React?”
    • “What is the difference between React and Angular?”
    • “Can you tell me the difference between Angular and React.js?”

  6. What can cause unnecessary re-renders in a React application?

    Asked in 4 of 1,028 interviews · last asked Oct 3 · Concept · Mid-level

    Other ways it was asked
    • “What can cause excessive renders in a React application?”
    • “How can you prevent unnecessary re-renders in React?”
    • “How can you prevent unnecessary re-renders in a React application?”

  7. How do you pass data from a parent component to a child component in Angular?

    Asked in 4 of 1,028 interviews · last asked Sep 29 · Concept · Junior

    Other ways it was asked
    • “How can you pass data from a parent component to a child component in Angular?”
    • “In Angular, how do you pass data to a child component, and how does the child notify the parent about an event?”
    • “How do you pass data between components in Angular?”

Backend API and security interview questions

Backend questions cover frameworks, request handling, HTTP, REST, GraphQL, serialization, authentication, authorization, and application security. 823 questions.

  1. What’s the difference between authentication and authorization?

    Asked in 11 of 1,028 interviews · last asked Oct 23 · Concept · Junior

    Other ways it was asked
    • “What is the difference between authentication and authorization?”
    • “What is the difference between authorization and authentication?”
    • “What is the difference between authentication and authorization in APIs?”

  2. What is a REST API?

    Asked in 11 of 1,028 interviews · last asked Oct 5 · Concept · Junior

    Other ways it was asked
    • “What are REST APIs?”
    • “What do you mean by a RESTful API?”
    • “What is a REST API, and how would you implement one?”

  3. What are the common HTTP methods, and what is each used for in REST APIs?

    Asked in 10 of 1,028 interviews · last asked Oct 23 · Concept · Junior

    Other ways it was asked
    • “What are the main HTTP verbs commonly used in APIs?”
    • “What HTTP methods are available in an API?”
    • “Can you name some common HTTP methods?”

  4. What do you consider when designing a REST API?

    Asked in 9 of 1,028 interviews · last asked Oct 16 · Concept · Mid-level

    Other ways it was asked
    • “How do you design and develop a RESTful API?”
    • “What factors do you consider when designing or consuming REST APIs?”
    • “What are the best practices for designing a REST API?”

  5. How is GraphQL different from REST?

    Asked in 8 of 1,028 interviews · last asked Oct 22 · Concept · Mid-level

    Other ways it was asked
    • “What are the differences between GraphQL and REST?”
    • “What problem does GraphQL solve compared with REST APIs?”
    • “What is the difference between GraphQL and REST?”

  6. How do you secure a REST API?

    Asked in 7 of 1,028 interviews · last asked Oct 16 · Scenario · Senior

    Other ways it was asked
    • “How do you secure a web API?”
    • “How do you secure an API?”
    • “What mechanisms would you use to secure a REST API?”

  7. Can you explain Spring Boot?

    Asked in 7 of 1,028 interviews · last asked Oct 1 · Concept · Junior

    Other ways it was asked
    • “What is Spring Boot?”
    • “What is Spring Boot? Can you give me an example?”
    • “What is a Spring Boot application?”

  8. What is the difference between GET and POST?

    Asked in 7 of 1,028 interviews · last asked Aug 20 · Concept · Junior

    Other ways it was asked
    • “What is the difference between the GET and POST methods in an HTML form?”
    • “What is the difference between GET and POST methods in PHP?”
    • “What is the difference between GET and POST in HTTP?”

  9. What is the difference between Spring Framework and Spring Boot?

    Asked in 6 of 1,028 interviews · last asked Oct 16 · Concept · Junior

    Other ways it was asked
    • “What is the difference between Spring and Spring Boot?”
    • “What is the difference between the Spring Framework and Spring Boot?”
    • “How does Spring Boot differ from Spring, and what benefits does Spring Boot provide?”

  10. What is a SQL injection vulnerability? What is its impact, and how can it be prevented?

    Asked in 4 of 1,028 interviews · last asked Oct 17 · Concept · Mid-level

    Other ways it was asked
    • “What is SQL injection, how can an attacker exploit it, and how can it be prevented?”
    • “What is a SQL injection vulnerability? What is the impact, and how can it be prevented?”
    • “What is SQL injection?”

  11. Can you explain the Spring bean life cycle?

    Asked in 4 of 1,028 interviews · last asked Oct 16 · Concept · Mid-level

    Other ways it was asked
    • “What is the lifecycle of a Spring bean?”
    • “What is the Spring bean lifecycle?”
    • “Can you explain the bean life cycle?”

  12. How do offset pagination and cursor pagination differ?

    Asked in 4 of 1,028 interviews · last asked Oct 14 · Concept · Mid-level

    Other ways it was asked
    • “What is the difference between using an offset and a cursor for database pagination?”
    • “Explain the trade-offs between offset pagination and cursor pagination.”
    • “What is the difference between page-based pagination and cursor-based pagination?”
Show 5 more

  1. What is pagination?

    Asked in 4 of 1,028 interviews · last asked Sep 30 · Concept · Junior

    Other ways it was asked
    • “What do you mean by pagination?”
    • “What is pagination, and when would you use it?”
    • “What is pagination in PostgreSQL?”

  2. What's the difference between encryption and hashing?

    Asked in 3 of 1,028 interviews · last asked Sep 21 · Concept · Junior

    Other ways it was asked
    • “What is the difference between encryption and hashing?”
    • “How is hashing different from encryption?”

  3. What is the difference between SOAP and REST?

    Asked in 3 of 1,028 interviews · last asked Oct 15 · Concept · Junior

    Other ways it was asked
    • “What is the difference between REST and SOAP?”
    • “How do SOAP and REST differ, and in what situations would you choose each?”

  4. What is CORS, and how does it affect cross-origin requests?

    Asked in 3 of 1,028 interviews · last asked Sep 16 · Concept · Mid-level

    Other ways it was asked
    • “What is CORS?”
    • “What is CORS, and how does it work?”

  5. What is a JSON Web Token (JWT), and what types of JWTs are there?

    Asked in 3 of 1,028 interviews · last asked Sep 29 · Concept · Junior

    Other ways it was asked
    • “What is a JSON Web Token (JWT)?”
    • “What is a JSON Web Token (JWT), and what is it used for?”

SQL and database interview questions

Database questions range from SQL queries and joins to data models, indexes, transactions, query speed, and SQL versus NoSQL choices. 661 questions.

  1. How do SQL and NoSQL databases differ, using MongoDB as an example?

    Asked in 11 of 1,028 interviews · last asked Oct 23 · Concept · Junior

    Other ways it was asked
    • “What is the difference between SQL and NoSQL databases?”
    • “What is the key difference between SQL and NoSQL databases?”
    • “What is the main difference between a SQL and NoSQL database?”

  2. Write a SQL query to find the second-highest salary.

    Asked in 7 of 1,028 interviews · last asked Oct 22 · Write code · Junior

    Other ways it was asked
    • “Write an SQL query to find the third-highest employee salary.”
    • “Write a MySQL query to get the second highest salary from an employee table with only one salary column.”
    • “Can you write a SQL query to find the second-highest salary?”

  3. How would you optimize a slow-running SQL query?

    Asked in 7 of 1,028 interviews · last asked Oct 14 · Scenario · Mid-level

    Other ways it was asked
    • “What can you do to improve the performance of a slow SQL query?”
    • “How would you optimize a slow query?”
    • “How can you optimize a slow SQL query?”

  4. When would you choose PostgreSQL over MongoDB?

    Asked in 7 of 1,028 interviews · last asked Sep 29 · Concept · Mid-level

    Other ways it was asked
    • “How would you explain the difference between using MongoDB and PostgreSQL for a project, and when would you choose one over the other?”
    • “Why did you choose PostgreSQL over MongoDB?”
    • “Which do you prefer, MongoDB or PostgreSQL, and why?”

  5. What does the ACID acronym stand for in database transactions?

    Asked in 7 of 1,028 interviews · last asked Oct 7 · Concept · Junior

    Other ways it was asked
    • “What does ACID mean in the context of databases?”
    • “What are the ACID properties in database transactions?”
    • “What are the ACID properties of a database transaction?”

  6. What's the difference between WHERE and HAVING?

    Asked in 6 of 1,028 interviews · last asked Oct 13 · Concept · Junior

    Other ways it was asked
    • “What is the difference between WHERE and HAVING?”
    • “What is the difference between WHERE and HAVING clauses in SQL?”
    • “What is the difference between WHERE and HAVING in SQL?”

  7. What is the difference between a primary key and a unique constraint?

    Asked in 5 of 1,028 interviews · last asked Oct 16 · Concept · Junior

    Other ways it was asked
    • “What is the difference between a primary key and a unique key?”
    • “What is the difference between a unique key and a primary key?”
    • “In a relational database, what's the difference between a primary key and a unique constraint, and when would you use each?”

  8. What is the difference between DELETE, TRUNCATE, and DROP?

    Asked in 5 of 1,028 interviews · last asked Oct 16 · Concept · Junior

    Other ways it was asked
    • “Could you explain the difference between DELETE, TRUNCATE, and DROP in SQL?”
    • “What is the difference between TRUNCATE and DELETE?”
    • “What is the difference between DROP and TRUNCATE?”

  9. What are the disadvantages of database indexes?

    Asked in 5 of 1,028 interviews · last asked Sep 21 · Concept · Mid-level

    Other ways it was asked
    • “What are the drawbacks of using database indexes?”
    • “What are the disadvantages of using an index?”
    • “What are the disadvantages of using indexing?”

  10. What is database normalization?

    Asked in 5 of 1,028 interviews · last asked Oct 7 · Concept · Junior

    Other ways it was asked
    • “What is database normalization, and when would you use it?”
    • “What is database normalization, and why is it needed?”

  11. What are stored procedures, and when would you use them?

    Asked in 5 of 1,028 interviews · last asked Oct 16 · Concept · Junior

    Other ways it was asked
    • “What are SQL stored procedures, and when would you use them?”
    • “What are stored procedures?”
    • “What is a stored procedure in MySQL, and when would you use one?”

  12. Do you know the difference between clustered and non-clustered indexes in SQL Server?

    Asked in 4 of 1,028 interviews · last asked Oct 10 · Concept · Mid-level

    Other ways it was asked
    • “In SQL, what is the difference between clustered and nonclustered indexes?”
    • “What is the difference between clustered and nonclustered indexes?”
    • “What's the difference between a clustered and a non-clustered index?”
Show 5 more

  1. How do you determine which database columns should be indexed?

    Asked in 4 of 1,028 interviews · last asked Sep 28 · Scenario · Mid-level

    Other ways it was asked
    • “How do you determine which database indexes to create and which columns to index?”
    • “Which database columns would you index, and how would you decide?”
    • “How would you choose which columns to index in a database?”

  2. What are SQL execution plans, and how can you use them to investigate query performance?

    Asked in 4 of 1,028 interviews · last asked Oct 22 · Concept · Mid-level

    Other ways it was asked
    • “What is a SQL execution plan, and how do you use it to investigate query performance?”
    • “How do you use SQL execution plans to diagnose and optimize queries?”
    • “How do you read a SQL execution plan, and what information can it provide?”

  3. What are database triggers, and when would you use them?

    Asked in 3 of 1,028 interviews · last asked Sep 4 · Concept · Mid-level

    Other ways it was asked
    • “What is a database trigger, and when would you use one?”
    • “What are some use cases for database triggers?”
    • “What types of database triggers are there?”

  4. What is the difference between pessimistic locking and optimistic locking?

    Asked in 3 of 1,028 interviews · last asked Oct 12 · Concept · Mid-level

    Other ways it was asked
    • “What is the difference between pessimistic and optimistic locking?”
    • “How do optimistic and pessimistic locking work?”

  5. What is the difference between a primary key and a foreign key?

    Asked in 3 of 1,028 interviews · last asked Sep 6 · Concept · Junior

    Other ways it was asked
    • “What's the difference between a primary key and a foreign key? Give an example and why we'd use one.”

All SQL interview questions

System design and distributed systems interview questions

System design questions cover scaling services, microservices, messaging, caching, idempotency, consistency, multitenancy, networking, and handling failures. 917 questions.

  1. What is idempotency, and why is it useful for HTTP requests?

    Asked in 9 of 1,028 interviews · last asked Oct 16 · Concept · Mid-level

    Other ways it was asked
    • “Which HTTP methods are idempotent?”
    • “What is idempotency?”
    • “What is idempotency, and where is it useful in a software system?”

  2. How do microservices communicate with each other?

    Asked in 8 of 1,028 interviews · last asked Oct 23 · Concept · Mid-level

    Other ways it was asked
    • “What are the ways microservices can communicate with each other?”
    • “How does communication between two microservices happen?”
    • “How do microservices communicate with one another?”

  3. What is the difference between horizontal and vertical scaling, and when would you use each?

    Asked in 7 of 1,028 interviews · last asked Oct 22 · Concept · Mid-level

    Other ways it was asked
    • “What is the difference between vertical and horizontal scaling?”
    • “What is the difference between horizontal and vertical scaling?”
    • “What is the biggest difference between horizontal scaling and vertical scaling?”

  4. How would you design a rate limiter for a public API?

    Asked in 7 of 1,028 interviews · last asked Oct 16 · Design · Senior

    Other ways it was asked
    • “How would you implement the rate limiter?”
    • “How do you design a rate limiter?”
    • “How would you implement a rate limiter for APIs?”

  5. If a service restarts and an external service resends the same message for a 50,000-peso payment, how would you design the system so the recipient is not credited 100,000 pesos?

    Asked in 6 of 1,028 interviews · last asked Oct 15 · Design · Senior

    Other ways it was asked
    • “If a service restarts and an external service resends the same message for a 50,000-peso payment, how would you prevent the recipient from receiving 100,000 pesos?”
    • “If an external service resends the same 50,000-peso payment message after your service restarts, how would you prevent the recipient from receiving the payment twice?”
    • “How would you design the system so that if a service restarts and an external service resends the same 50,000-peso credit message, the customer is not credited twice? How would you handle a late event indicating that the transaction is already settled or in an intermediate state?”

  6. What is the Saga pattern in microservices, and when would you use it?

    Asked in 5 of 1,028 interviews · last asked Oct 16 · Concept · Senior

    Other ways it was asked
    • “What is the Saga design pattern in microservices, and when would you use it?”
    • “What is the core idea behind the Saga pattern in microservices architecture?”
    • “What is the saga pattern?”

  7. How do you design and build microservices?

    Asked in 5 of 1,028 interviews · last asked Jul 31 · Design · Mid-level

    Other ways it was asked
    • “What are the key considerations when designing a microservices architecture?”
    • “What are some key factors to consider when designing scalable microservices?”
    • “How do you design and implement microservices?”

  8. How would you design a payment processing system?

    Asked in 5 of 1,028 interviews · last asked Oct 9 · Design · Mid-level

    Other ways it was asked
    • “How would you implement payment processing?”
    • “How would you implement payment processing in an application?”
    • “How would you design a payment system?”

  9. What are the differences between Kafka and RabbitMQ?

    Asked in 4 of 1,028 interviews · last asked Sep 16 · Concept · Mid-level

    Other ways it was asked
    • “What is the difference between Kafka and RabbitMQ?”
    • “What are the implementation differences between Kafka and RabbitMQ, and how do you decide which one to use?”
    • “What is the key difference between Kafka and RabbitMQ?”

  10. How would you implement idempotency end to end? Where would you store the idempotency key, how would you validate it per user, and what would you return for a repeated request?

    Asked in 4 of 1,028 interviews · last asked Oct 17 · Design · Senior

    Other ways it was asked
    • “How would you implement idempotency for a charge-customer call? What idempotency key strategy would you use, where would you persist it, and what would you return for a repeated request?”
    • “How would you implement idempotency in an application?”
    • “How would you implement idempotency across steps in an integration? What key would you use, where would you store it, and how would you handle concurrent duplicate requests?”

  11. What is Redis, and how would you use it in an application?

    Asked in 3 of 1,028 interviews · last asked Oct 12 · Tooling · Junior

    Other ways it was asked
    • “How can Redis be used in an application?”
    • “What is Redis, and why do we need to use it in our application?”

  12. What is the difference between synchronous and asynchronous communication between services?

    Asked in 3 of 1,028 interviews · last asked Oct 23 · Concept · Mid-level

    Other ways it was asked
    • “How would you decide whether to use synchronous or asynchronous communication between services?”
    • “What is the difference between synchronous and asynchronous services, and when would you use each?”
Show 7 more

  1. How would you design a multi-tenant ERP architecture?

    Asked in 3 of 1,028 interviews · last asked Oct 7 · Design · Senior

    Other ways it was asked
    • “How would you design a multi-tenant architecture?”
    • “Explain your multi-tenant ERP architecture.”

  2. What is caching?

    Asked in 3 of 1,028 interviews · last asked Oct 12 · Concept · Junior

    Other ways it was asked
    • “What is caching, and how does it work?”
    • “What is caching, and when would you use it?”

  3. What is multitenancy?

    Asked in 3 of 1,028 interviews · last asked Jul 16 · Concept · Junior

    Other ways it was asked
    • “What is multitenancy in application design?”
    • “What is multitenancy, and what is it used for?”

  4. How would you implement caching in an application, and when would you use it?

    Asked in 3 of 1,028 interviews · last asked Oct 12 · Concept · Mid-level

    Other ways it was asked
    • “How would you implement caching in an application?”
    • “What caching techniques would you use in a web application?”

  5. What is the role of an API gateway?

    Asked in 3 of 1,028 interviews · last asked Oct 1 · Concept · Mid-level

    Other ways it was asked
    • “What problem does an API gateway solve?”
    • “Why do we need an API gateway?”
    • “What is the purpose of a REST API gateway?”

  6. What is eventual consistency?

    Asked in 2 of 1,028 interviews · last asked Oct 15 · Concept · Mid-level

    Other ways it was asked
    • “What is eventual consistency, and where might users notice it?”

  7. What is a cascading failure?

    Asked in 2 of 1,028 interviews · last asked Oct 6 · Concept · Mid-level

    Other ways it was asked
    • “How can you solve cascading failures?”

All System Design interview questions

AI and LLM interview questions for software engineers

AI questions explore development tools, checking generated code, agents, RAG systems, automation, and protecting sensitive data. 234 questions.

  1. How would you implement a retrieval-augmented generation (RAG) system?

    Asked in 5 of 1,028 interviews · last asked Sep 30 · Design · Mid-level

    Other ways it was asked
    • “Can you explain retrieval-augmented generation (RAG) in simpler terms?”
    • “What is retrieval-augmented generation (RAG), and how is it used in data-related projects?”
    • “How does a retrieval-augmented generation (RAG) system work, step by step?”

  2. What are AI agents, and when would you use them?

    Asked in 3 of 1,028 interviews · last asked Oct 16 · Concept · Mid-level

    Other ways it was asked
    • “What are AI agent skills, and when would you use them?”
    • “How do you use AI agents?”
    • “What are AI agents, and how can they be used in a software development workflow, particularly for coding?”

  3. How do you evaluate the quality of AI-generated code before using it?

    Asked in 3 of 1,028 interviews · last asked Oct 20 · Scenario · Senior

    Other ways it was asked
    • “What are the potential pitfalls you have encountered with AI-generated code, and how do you ensure the quality of the code generated?”
    • “What should you consider when using AI-generated code?”

  4. What are the main components of a RAG system?

    Asked in 3 of 1,028 interviews · last asked Sep 30 · Concept · Mid-level

    Other ways it was asked
    • “What is RAG?”
    • “What is a RAG system, and when would you use one?”
    • “What problems can a RAG system address, and why would you implement one?”

  5. How do you use AI coding tools like Claude Code and Copilot in your day-to-day work?

    Asked in 2 of 1,028 interviews · last asked Sep 23 · Tooling · Mid-level

    Other ways it was asked
    • “How do you use AI coding assistants such as GitHub Copilot and Claude, and what tasks do you use them for?”

  6. How would you build an AI agent?

    Asked in 2 of 1,028 interviews · last asked Sep 9 · Design · Mid-level

    Other ways it was asked
    • “What components are needed to build an AI agent?”
    • “How do you build an AI agent and define its workflows?”
    • “How do you define workflows for AI agents?”

  7. How would a traditional rule-based solution to distinguish apples from oranges compare with a machine learning-based solution?

    Asked in 2 of 1,028 interviews · last asked May 7 · Concept · Junior

    Other ways it was asked
    • “How would you implement a program to distinguish apples from oranges using traditional methods, and how would you approach it with machine learning?”

  8. What is an LLM?

    Asked in 2 of 1,028 interviews · last asked Oct 22 · Concept · Junior

    Other ways it was asked
    • “Could you explain what an LLM is?”

  9. What is a large language model?

    Asked in 2 of 1,028 interviews · last asked Oct 22 · Concept · Junior

    Other ways it was asked
    • “What are large language models, and what are they used for?”
    • “What are some major large language models currently available?”

  10. What are skills in AI agents, and how are they used?

    Asked in 2 of 1,028 interviews · last asked Sep 7 · Concept · Mid-level

    Other ways it was asked
    • “What is a skill in an AI agent?”

  11. How do you write effective prompts for AI systems?

    Asked in 2 of 1,028 interviews · last asked Oct 16 · Concept · Mid-level

    Other ways it was asked
    • “How do you write prompts for AI tools to support software development?”

  12. What is a recommendation system?

    Asked in 2 of 1,028 interviews · last asked Sep 28 · Concept · Junior

    Other ways it was asked
    • “How does a recommendation system work?”
Show 7 more

  1. Do you use any AI tools like ChatGPT or similar? How do you use them and how do you keep up with what is new?

    Asked in 2 of 1,028 interviews · last asked Aug 10 · Tooling

    Other ways it was asked
    • “How do you use ChatGPT or other AI tools when developing an application?”

  2. How do you choose an AI model when generating code or tests with a coding assistant?

    Asked in 2 of 1,028 interviews · last asked Oct 9 · Tooling · Mid-level

    Other ways it was asked
    • “How do you decide when to write code yourself versus use an AI coding assistant?”

  3. Which metrics would you use to evaluate an AI agent?

    Asked once · last asked Jun 18 · Concept · Senior

    Other ways it was asked
    • “Which metrics would you use to measure an AI agent's effectiveness?”

  4. How is OCR integration used in an application?

    Asked once · last asked Jun 18 · Tooling · Mid-level

    Other ways it was asked
    • “What is OCR integration?”

  5. When would you use supervised rather than unsupervised learning for a recommendation model?

    Asked once · last asked Sep 28 · Concept · Mid-level

    Other ways it was asked
    • “How would you use supervised learning to train a recommendation model?”
    • “Why might supervised learning be a better choice than unsupervised learning for a recommendation model?”
    • “How do supervised learning and reinforcement learning differ when building a recommendation model?”

  6. How would you design the tools and data pipeline for an AI scorecard agent?

    Asked once · last asked Jul 25 · Design · Senior

    Other ways it was asked
    • “What model and overall architecture would you use for an AI scorecard agent?”

  7. How does an MCP agent select a forecasting model?

    Asked once · last asked Aug 24 · Concept · Senior

Software testing, DevOps, and behavioral interview questions

Questions about daily engineering work cover testing, debugging, code reviews, Git, CI/CD, deployments, monitoring, requirements, teamwork, and delivery decisions. 1,184 questions.

  1. How would you design a CI/CD pipeline?

    Asked in 5 of 1,028 interviews · last asked Oct 23 · Design · Mid-level

    Other ways it was asked
    • “What are the main stages of a CI/CD pipeline?”
    • “How do you implement a CI/CD pipeline, and how does it work?”
    • “How would you integrate CI/CD into a software delivery pipeline?”

  2. How do you ensure the quality of the code your team delivers?

    Asked in 5 of 1,028 interviews · last asked Oct 1 · Behavioral · Senior

    Other ways it was asked
    • “How do you ensure code quality across your team?”
    • “How do you ensure the quality of the team's work and code?”
    • “How do you ensure code quality?”

  3. What is the difference between Git merge and Git rebase?

    Asked in 4 of 1,028 interviews · last asked Oct 7 · Concept · Junior

    Other ways it was asked
    • “What is the difference between merging and rebasing in Git?”
    • “What is the difference between Git merge and Git rebase, when would you use each, and what should you avoid?”

  4. How would you respond if you were assigned work involving a technology you had not used before?

    Asked in 4 of 1,028 interviews · last asked Oct 20 · Scenario

    Other ways it was asked
    • “How would you respond if you were assigned a technology you had never used before?”
    • “How would you approach being assigned a technology you have never used before?”
    • “What would you do first if you were assigned a task involving technology you had never used before?”

  5. What is Test-Driven Development, and when would you use it?

    Asked in 4 of 1,028 interviews · last asked Jun 25 · Concept · Mid-level

    Other ways it was asked
    • “How does Test-Driven Development work in practice?”
    • “Can you briefly explain what Test-Driven Development is and what its core idea is?”
    • “What is test-driven development (TDD), and how does it guide the development process?”

  6. What do you look for when reviewing code?

    Asked in 3 of 1,028 interviews · last asked May 26 · Concept · Mid-level

    Other ways it was asked
    • “What do you prioritize when reviewing code?”

  7. What are the fundamental differences between Waterfall and Agile?

    Asked in 3 of 1,028 interviews · last asked Aug 27 · Concept · Junior

    Other ways it was asked
    • “How do you compare waterfall and agile development?”
    • “How do waterfall and agile development differ?”
    • “Can you explain the Agile and Waterfall methodologies?”

  8. How do you respond when a team member is falling behind schedule?

    Asked in 3 of 1,028 interviews · last asked May 26 · Scenario · Mid-level

    Other ways it was asked
    • “How would you respond if a team member were falling behind schedule?”
    • “How would you respond if a team member fell behind schedule?”

  9. What is CI/CD?

    Asked in 3 of 1,028 interviews · last asked Mar 2 · Concept · Junior

    Other ways it was asked
    • “What is CI/CD, and how does it fit into deploying code to production?”

  10. What is Docker, and what is it used for?

    Asked in 3 of 1,028 interviews · last asked Aug 25 · Concept · Junior

    Other ways it was asked
    • “What is Docker?”
    • “What are Docker and containers?”

  11. How do you bring structure to a chaotic project?

    Asked in 3 of 1,028 interviews · last asked May 11 · Scenario · Mid-level

    Other ways it was asked
    • “How do you typically handle a work environment that isn't very organized, and how do you bring structure to a chaotic project?”

  12. What is GitHub?

    Asked in 3 of 1,028 interviews · last asked Aug 27 · Concept · Junior

Show 8 more

  1. What is Docker Compose used for?

    Asked in 3 of 1,028 interviews · last asked Oct 15 · Concept · Junior

    Other ways it was asked
    • “What is Docker Compose, and what is it used for?”
    • “How does Docker Compose work?”

  2. What are end-to-end tests?

    Asked in 3 of 1,028 interviews · last asked Sep 21 · Concept · Junior

    Other ways it was asked
    • “What are end-to-end tests, and when should you use them?”
    • “How do you implement end-to-end tests in code?”

  3. Tell me about a technically challenging project, the challenges you faced, and the decisions and trade-offs you made to resolve them.

    Asked in 2 of 1,028 interviews · last asked Oct 9 · Behavioral · Mid-level

    Other ways it was asked
    • “Tell me about a technically challenging project, what you were trying to accomplish, and why.”

  4. If an API suddenly goes slow in production and customers start complaining, what’s your step-by-step approach?

    Asked in 2 of 1,028 interviews · last asked Sep 1 · Scenario · Senior

    Other ways it was asked
    • “Imagine a production API is slow and users are complaining. What's your step-by-step approach to investigate?”
    • “If an API is slow in production, what do you do first and how do you proceed?”

  5. What tools would you use for A/B testing?

    Asked in 2 of 1,028 interviews · last asked Oct 16 · Scenario · Mid-level

    Other ways it was asked
    • “How do you conduct an A/B test?”
    • “How have you used A/B testing, and how did you evaluate the results?”
    • “How would you design a minimal A/B test?”

  6. What is the difference between unit tests and integration tests?

    Asked in 2 of 1,028 interviews · last asked Oct 7 · Concept · Junior

    Other ways it was asked
    • “What is the difference between a unit test and an integration test?”

  7. What is the difference between a Dockerfile and Docker Compose?

    Asked in 2 of 1,028 interviews · last asked Aug 25 · Concept · Junior

    Other ways it was asked
    • “What is the difference between Docker and Docker Compose?”

  8. How would you investigate the cause of a slow application?

    Asked in 2 of 1,028 interviews · last asked May 11 · Scenario · Mid-level

    Other ways it was asked
    • “When an application becomes slow, how would you identify the root cause?”
    • “What are some common causes of a slow application?”

Live coding round next? Coding mode in the MeetAssist desktop app solves the problem on your screen, with your phone as the remote.

How this list is made

Every question here was asked by a real interviewer in a real job interview that a candidate ran MeetAssist in. After the call, the interviewer's questions are pulled from the transcript. Practice sessions, tests, exams and anything that was not a job interview are dropped.

Questions are rewritten so they make sense on their own: names of people, employers and clients are removed, and speech-to-text mistakes are fixed. Small talk, logistics and questions about one candidate's own résumé are left out. Rephrasings of the same question are merged, and the count is the number of different interviews it came up in.

The interviews come from candidates who use MeetAssist, so they lean towards software, data and AI roles: the shares describe these interviews, not every Software Engineer interview. Answers to the most asked questions are written and checked by an editor; a "common mistake" is shown only when reviews of real answers in these interviews show it, with the count.

1,028 interviews, 539 candidates, Sep 2025 to Oct 2026. Updated every month with new interviews.