Top 30 Most Common Karat Interview Questions You Should Prepare For
Written by
James Miller, Career Coach
Introduction
Preparing for a Karat interview is a crucial step for any software engineer looking to land a position at top tech companies that use Karat's interviewing platform. Unlike traditional interviews, Karat specialises in conducting technical screens focused on core computer science fundamentals, data structures, algorithms, and practical coding skills. They provide a standardized, efficient process designed to accurately assess a candidate's technical proficiency in a live coding environment, often involving challenging problems. Success in a Karat interview hinges on solid theoretical knowledge combined with the ability to translate that knowledge into clean, working code under pressure. This guide delves into 30 common karat interview questions spanning essential areas, offering insights and preparation strategies to help you confidently navigate the process and demonstrate your engineering competence. Mastering these types of karat interview questions is key to advancing to subsequent interview rounds with the hiring company.
What Are Karat Interviews?
Karat interviews are technical interviews conducted by experienced engineers via a video call platform, acting as the initial screening phase for many tech companies. They are designed to provide a consistent and objective assessment of a candidate's fundamental software engineering skills, particularly in coding and problem-solving. The typical format involves one or two coding challenges presented in a shared editor, where candidates must explain their thought process, write functional code, and discuss time/space complexity. These interviews evaluate a candidate's ability to think algorithmically, utilise data structures effectively, and produce robust solutions. Karat aims to make the interview process more efficient and equitable for both companies and candidates by standardising the technical evaluation, ensuring candidates face similar levels of difficulty and assessment criteria.
Why Do Interviewers Ask These Questions?
Karat interview questions are carefully selected to probe a candidate's foundational knowledge and practical skills relevant to a software engineering role. Interviewers ask data structure and algorithm questions to evaluate problem-solving abilities, efficiency considerations (time/space complexity), and understanding of core computer science concepts. Coding challenges assess the ability to translate logic into working code, handle edge cases, and write clean, maintainable solutions under timed conditions. System design questions, often included for more senior roles, gauge understanding of scalable and distributed systems, architectural choices, and trade-offs. Concurrency and fundamental concepts like processes, threads, and memory management test understanding of how software operates at a deeper level. Collectively, these karat interview questions paint a comprehensive picture of a candidate's technical readiness for the demands of a software engineering position.
Preview List
Explain the difference between a linked list and an array.
How do you detect a cycle in a linked list?
Describe the time complexity of quicksort and when it performs poorly.
Implement a function to reverse a binary tree.
What is a race condition? How do you prevent it?
Explain memoization and give an example.
Write a function to find the kth largest element in an unsorted array.
What are the differences between processes and threads?
Explain the concept of dynamic programming.
Given a matrix of 0s and 1s, find the largest square containing only 1s.
How would you design a URL shortening service?
What is a memory leak and how can it be detected?
Explain the difference between a stack and a queue.
Write code to check if a string has all unique characters.
What are hash tables and how do they work?
Describe how garbage collection works.
What is the difference between abstraction and encapsulation?
Explain how you would test an API endpoint.
Write a function to merge two sorted linked lists.
What is a deadlock? How can it be prevented?
Describe the SOLID principles in object-oriented design.
How do you find the first non-repeated character in a string?
Explain the difference between synchronous and asynchronous programming.
What are design patterns? Give examples.
How would you optimize a slow SQL query?
Implement a breadth-first search (BFS) in a graph.
Explain how HTTPS works.
What is polymorphism in OOP?
How do you handle errors in code?
Describe the CAP theorem.
1. Explain the difference between a linked list and an array.
Why you might get asked this:
Fundamental data structure question assessing knowledge of memory allocation, access patterns, and performance trade-offs.
How to answer:
Compare based on memory layout (contiguous vs. nodes), access time (O(1) vs. O(n)), size flexibility (fixed vs. dynamic), and insertion/deletion costs.
Example answer:
An array uses contiguous memory, offering O(1) random access by index but fixed size. A linked list uses nodes with pointers, enabling dynamic sizing and O(1) insertions/deletions (if pointer is known) but O(n) access for a specific index.
2. How do you detect a cycle in a linked list?
Why you might get asked this:
Tests understanding of pointers, linked list traversal, and algorithm design for detecting structural issues.
How to answer:
Describe the Floyd's Cycle Detection Algorithm (tortoise and hare) using two pointers at different speeds. If they meet, a cycle exists.
Example answer:
Use two pointers, 'slow' and 'fast'. Slow moves one step at a time, fast moves two. If the list has a cycle, the fast pointer will eventually catch up to and meet the slow pointer within the cycle.
3. Describe the time complexity of quicksort and when it performs poorly.
Why you might get asked this:
Evaluates understanding of sorting algorithms, recursion, average/worst-case performance, and pivot selection impact.
How to answer:
State average O(n log n) and worst-case O(n²). Explain the worst-case occurs with poor pivot choices on sorted/reverse-sorted data.
Example answer:
Quicksort's average time complexity is O(n log n), highly efficient. Its worst-case is O(n²), which happens when the pivot consistently results in unbalanced partitions, like picking the smallest or largest element in an already sorted array.
4. Implement a function to reverse a binary tree.
Why you might get asked this:
Tests recursive thinking and ability to manipulate tree structures.
How to answer:
Explain the recursive approach: swap the left and right children of the current node, then recursively call the function on the new left and right children.
Example answer:
The function would take a node. If the node is null, return. Otherwise, swap node.left and node.right. Then, recursively call the function on node.left (which was originally node.right) and node.right (originally node.left).
5. What is a race condition? How do you prevent it?
Why you might get asked this:
Assesses understanding of concurrency issues and mechanisms for safe multi-threaded programming.
How to answer:
Define a race condition as simultaneous access to shared resources leading to unpredictable results. Prevention involves synchronisation mechanisms.
Example answer:
A race condition occurs when multiple threads access shared data concurrently, and the final outcome depends on the unpredictable order of operations. Prevent by using locks, mutexes, semaphores, or atomic operations to ensure mutual exclusion for critical sections.
6. Explain memoization and give an example.
Why you might get asked this:
Evaluates understanding of optimisation techniques for recursive algorithms involving overlapping subproblems.
How to answer:
Define memoization as caching function call results to avoid recomputing for the same inputs. Provide a classic recursive example.
Example answer:
Memoization is an optimisation technique where results of expensive function calls are stored and returned when the same inputs occur again. Example: Calculating Fibonacci numbers recursively; store fib(n) in a map after computing it to avoid redundant calculations for nested calls.
7. Write a function to find the kth largest element in an unsorted array.
Why you might get asked this:
Common algorithm problem testing knowledge of selection algorithms or data structures like heaps.
How to answer:
Suggest using a min-heap of size k or the Quickselect algorithm. Discuss their respective time complexities.
Example answer:
One approach is using a min-heap of size k. Iterate through the array, pushing elements onto the heap. If the heap size exceeds k, pop the smallest element. The heap's root after processing the array is the kth largest. Quickselect offers an average O(n) solution.
8. What are the differences between processes and threads?
Why you might get asked this:
Core operating system concept knowledge testing understanding of execution units and resource sharing.
How to answer:
Distinguish based on memory space (separate vs. shared), overhead (high vs. low), creation time, and communication methods.
Example answer:
A process is an instance of a program with its own isolated memory space and resources. Threads are units of execution within a process, sharing the same memory space and resources. Processes have higher creation/switching overhead than threads.
9. Explain the concept of dynamic programming.
Why you might get asked this:
Assesses understanding of a powerful technique for solving complex problems by breaking them into smaller, overlapping parts.
How to answer:
Define DP as solving problems by breaking them into overlapping subproblems and storing results (memoization or tabulation) to avoid recomputation.
Example answer:
Dynamic programming is a method for solving complex problems by breaking them down into simpler overlapping subproblems. The results of these subproblems are stored (memoization or tabulation) to avoid recomputing them multiple times, leading to efficient solutions for problems with optimal substructure.
10. Given a matrix of 0s and 1s, find the largest square containing only 1s.
Why you might get asked this:
Classic 2D dynamic programming problem testing state definition and transition logic.
How to answer:
Explain the DP approach using a table to store the size of the largest square ending at each cell. The value at cell (i, j) depends on (i-1, j), (i, j-1), and (i-1, j-1).
Example answer:
Use a DP table dp[i][j] representing the size of the largest square ending at matrix[i][j]. If matrix[i][j] is 1, dp[i][j] is min(dp[i-1][j], dp[i][j-1], dp[i-1][j-1]) + 1. If 0, it's 0. Track the maximum value in the DP table.
11. How would you design a URL shortening service?
Why you might get asked this:
Systems design question assessing understanding of hashing, storage, collision handling, and scalability.
How to answer:
Discuss key components: hashing function for key generation, database for mapping storage, collision resolution strategies, and considerations for read/write throughput.
Example answer:
A URL shortening service involves generating a unique short key for a long URL using a hash function. Store the key-URL mapping in a database (e.g., key-value store). Handle hash collisions (e.g., increment counter, linear probing). Redirect requests using the short key to fetch the long URL. Consider scalability, data storage, and key uniqueness.
12. What is a memory leak and how can it be detected?
Why you might get asked this:
Tests understanding of memory management, resource handling, and debugging techniques.
How to answer:
Define memory leak as unreleased allocated memory. Detection methods include profiling tools and monitoring system resource usage over time.
Example answer:
A memory leak occurs when a program allocates memory but fails to release it when it's no longer needed, leading to gradual exhaustion of available memory. It can be detected using memory profiling tools (like Valgrind for C++, profilers in Java/Python) or by observing a steady increase in memory consumption over time.
13. Explain the difference between a stack and a queue.
Why you might get asked this:
Fundamental data structure knowledge, assessing understanding of LIFO and FIFO principles and common use cases.
How to answer:
Define each based on its primary access method: Stack is LIFO (Last-In, First-Out), Queue is FIFO (First-In, First-Out). Mention operations (push/pop vs. enqueue/dequeue).
Example answer:
A stack is a linear data structure following the LIFO principle; the last element added is the first one removed (like a stack of plates). A queue follows the FIFO principle; the first element added is the first one removed (like a waiting line).
14. Write code to check if a string has all unique characters.
Why you might get asked this:
Basic string manipulation problem testing use of data structures like hash sets or bit manipulation.
How to answer:
Suggest using a hash set (or boolean array if character set is small) to track seen characters. Iterate through the string and check for duplicates.
Example answer:
Use a hash set. Iterate through the string character by character. For each character, check if it's already in the set. If it is, return false. Otherwise, add the character to the set. If the loop finishes without finding duplicates, return true.
15. What are hash tables and how do they work?
Why you might get asked this:
Essential data structure knowledge, understanding key-value mapping, hashing, and collision resolution.
How to answer:
Define hash tables as structures storing key-value pairs using a hash function. Explain how hashing maps keys to array indices and mention collision handling methods (chaining, open addressing).
Example answer:
Hash tables (or hash maps) store key-value pairs. They use a hash function to compute an index in an array (buckets) where the value is stored. Access is typically O(1) on average. Collisions (different keys hashing to the same index) are handled using techniques like chaining (linked lists at each bucket) or open addressing (probing for the next available slot).
16. Describe how garbage collection works.
Why you might get asked this:
Tests understanding of automatic memory management in languages that support it.
How to answer:
Explain the purpose (automatic memory freeing) and general mechanisms like tracing reachability (marking and sweeping) or reference counting.
Example answer:
Garbage collection is an automatic process that reclaims memory no longer in use by a program. Common methods include tracing garbage collectors (mark and sweep, copying) that identify unreachable objects and reclaim their memory, and reference counting, which tracks references to objects and frees memory when the count drops to zero.
17. What is the difference between abstraction and encapsulation?
Why you might get asked this:
Object-oriented programming concepts testing understanding of principles for managing complexity and structuring code.
How to answer:
Distinguish abstraction as hiding complex implementation details and showing only essential features, while encapsulation bundles data and methods, controlling access to data.
Example answer:
Abstraction focuses on hiding complexity and showing only relevant details to the user (e.g., a car's steering wheel abstracts away the engine). Encapsulation bundles data and methods together within a unit (like a class) and controls access to the data, protecting its integrity.
18. Explain how you would test an API endpoint.
Why you might get asked this:
Practical software engineering skills testing understanding of testing methodologies and types.
How to answer:
Discuss unit testing (internal logic), integration testing (interactions), and end-to-end testing. Mention testing inputs, outputs, status codes, error handling, and using tools.
Example answer:
I would write automated tests covering different scenarios: unit tests for internal logic, integration tests for interactions with databases or other services, and potentially end-to-end tests. I'd test various inputs (valid, invalid, edge cases), verify correct output data, HTTP status codes, error responses, and performance under load. Tools like Postman or dedicated testing frameworks would be used.
19. Write a function to merge two sorted linked lists.
Why you might get asked this:
Linked list manipulation and merging sorted sequences, common coding problem.
How to answer:
Describe iterative approach using a dummy node and pointers to compare and append nodes from both lists until one is empty.
Example answer:
Create a dummy node to simplify edge cases and a pointer to track the merged list's tail. Iterate through both lists, comparing nodes and appending the smaller one to the merged list via the tail pointer. Advance the corresponding list pointer. Once one list is exhausted, append the rest of the other list. Return the next node of the dummy.
20. What is a deadlock? How can it be prevented?
Why you might get asked this:
Concurrency and operating systems concept testing understanding of resource contention issues.
How to answer:
Define deadlock as multiple processes/threads blocked indefinitely waiting for resources held by others. Mention prevention conditions (mutual exclusion, hold and wait, no preemption, circular wait) and strategies.
Example answer:
A deadlock occurs when two or more processes are waiting indefinitely for each other to release resources. It can be prevented by breaking one of the four necessary conditions: mutual exclusion (not always possible), hold and wait, no preemption, or circular wait (e.g., enforcing resource ordering).
21. Describe the SOLID principles in object-oriented design.
Why you might get asked this:
Tests knowledge of fundamental principles for writing maintainable, flexible, and scalable object-oriented code.
How to answer:
List and briefly explain each principle: Single responsibility, Open-closed, Liskov substitution, Interface segregation, Dependency inversion.
Example answer:
SOLID is an acronym for five principles: Single Responsibility (class has one job), Open-Closed (open for extension, closed for modification), Liskov Substitution (subtypes substitutable for base types), Interface Segregation (many specific interfaces better than one general), Dependency Inversion (depend on abstractions, not concretions).
22. How do you find the first non-repeated character in a string?
Why you might get asked this:
String manipulation problem testing use of hash maps for character frequency counting.
How to answer:
Suggest using a hash map to store character counts. Iterate once to count frequencies, then iterate again to find the first character with a count of 1.
Example answer:
Use a hash map (or dictionary) to store the frequency of each character in the string. Iterate through the string once to populate the map. Then, iterate through the string again. The first character encountered whose count in the map is 1 is the answer.
23. Explain the difference between synchronous and asynchronous programming.
Why you might get asked this:
Tests understanding of execution models, blocking vs. non-blocking operations, and handling I/O.
How to answer:
Explain synchronous execution as blocking, waiting for each operation to complete. Asynchronous execution is non-blocking, allowing other tasks to run while waiting for an operation to finish.
Example answer:
Synchronous execution means tasks are performed sequentially; each operation must complete before the next one starts. Asynchronous execution allows a program to initiate an operation (like I/O) and continue processing other tasks without waiting for the operation to finish, handling the result later via callbacks, promises, or async/await.
24. What are design patterns? Give examples.
Why you might get asked this:
Evaluates knowledge of common, reusable solutions to recurring software design problems.
How to answer:
Define design patterns as established solutions. Categorize and provide examples from common categories (creational, structural, behavioral).
Example answer:
Design patterns are reusable solutions to common problems encountered in software design. They are not concrete implementations but templates. Examples include: Creational (Singleton, Factory), Structural (Adapter, Decorator), and Behavioral (Observer, Strategy). They promote best practices and improve code readability.
25. How would you optimize a slow SQL query?
Why you might get asked this:
Practical database skills testing understanding of performance tuning techniques.
How to answer:
Suggest indexing, query analysis (EXPLAIN), avoiding SELECT *, limiting data retrieved, optimising joins, and database schema review.
Example answer:
To optimize a slow SQL query, I'd first analyze the query plan using EXPLAIN to identify bottlenecks. Key strategies include ensuring appropriate indexes exist on columns used in WHERE clauses, JOIN conditions, and ORDER BY clauses. Avoid SELECT *, retrieve only necessary columns. Optimize join order and minimize joins. Consider denormalization if reads are frequent.
26. Implement a breadth-first search (BFS) in a graph.
Why you might get asked this:
Fundamental graph traversal algorithm testing ability to use queues and manage visited nodes.
How to answer:
Describe using a queue and a visited set. Start with a node, add neighbors to queue, mark visited, process queue layer by layer.
Example answer:
BFS uses a queue and a set/array to track visited nodes. Start by adding the source node to the queue and marking it visited. While the queue isn't empty, dequeue a node, process it, and enqueue all its unvisited neighbors, marking them visited. This explores the graph layer by layer.
27. Explain how HTTPS works.
Why you might get asked this:
Web security and networking concepts testing understanding of encryption and secure communication.
How to answer:
Explain it's HTTP over TLS/SSL. Mention encryption, certificates for identity verification, and the handshake process.
Example answer:
HTTPS is the secure version of HTTP, using TLS/SSL encryption to secure communication between client and server. It involves a handshake process where the server proves its identity using a digital certificate, and a symmetric encryption key is established for secure data transfer. This ensures data confidentiality and integrity.
28. What is polymorphism in OOP?
Why you might get asked this:
Object-oriented programming concept testing understanding of how objects of different classes can respond to the same message.
How to answer:
Define polymorphism as "many forms," allowing objects of different classes to be treated as objects of a common superclass. Mention method overriding and overloading as examples.
Example answer:
Polymorphism means "many forms." In OOP, it allows objects of different classes to respond to the same method call in their own specific ways. Key types are compile-time (method overloading) and runtime (method overriding), where a superclass reference can point to a subclass object, and the appropriate method is called based on the actual object type.
29. How do you handle errors in code?
Why you might get asked this:
Tests understanding of robust programming practices, debugging, and maintaining application stability.
How to answer:
Discuss using exception handling (try-catch), input validation, logging, and providing informative error messages.
Example answer:
Error handling involves anticipating potential issues and gracefully managing them. I use exception handling mechanisms (try-catch or equivalent) to catch and handle runtime errors. Input validation is crucial to prevent errors caused by invalid data. Logging helps track errors for debugging. Providing clear, user-friendly error messages improves usability.
30. Describe the CAP theorem.
Why you might get asked this:
Distributed systems concept testing understanding of fundamental trade-offs in designing distributed databases/systems.
How to answer:
State the three components: Consistency, Availability, Partition tolerance. Explain that a distributed system can only guarantee two out of the three simultaneously during a network partition.
Example answer:
The CAP theorem states that a distributed database system cannot simultaneously guarantee Consistency, Availability, and Partition tolerance. During a network partition (loss of communication between nodes), you must choose between Consistency (all clients see the same data) and Availability (all clients can read/write). Most modern distributed systems prioritize Availability and Partition Tolerance, sacrificing immediate Consistency (eventual consistency).
Other Tips to Prepare for a Karat Interview
Success in karat interview questions requires focused preparation beyond just reviewing concepts. "Practice coding problems under timed conditions to simulate the interview environment," advises a seasoned hiring manager. Many candidates find that using an interactive platform significantly enhances their readiness. The Verve AI Interview Copilot (https://vervecopilot.com) offers realistic AI-powered interview simulations specifically designed for technical roles, allowing you to practice explaining your thought process and getting immediate feedback. Utilizing tools like the Verve AI Interview Copilot can help you refine your communication skills alongside your coding abilities. Remember to practice discussing the time and space complexity of your solutions, a critical part of the Karat evaluation. Leveraging practice resources like the Verve AI Interview Copilot is a smart strategy. As one candidate shared, "Running through mock interviews, especially on platforms like Verve AI Interview Copilot, made a huge difference in my confidence level for the actual karat interview."
Frequently Asked Questions
Q1: How long is a typical Karat interview? A1: Karat interviews usually last around 60 minutes, including coding and discussion.
Q2: What programming language should I use? A2: You can typically use any major language like Python, Java, C++, or JavaScript.
Q3: Are Karat interviews harder than typical interviews? A3: They are structured and rigorous, focusing purely on technical skill via live coding problems.
Q4: Do I need to prepare for system design? A4: System design is often included, especially for mid-level to senior karat interview questions.
Q5: What kind of feedback does Karat provide? A5: Karat provides a score or evaluation passed to the hiring company; direct candidate feedback varies by company policy.
Q6: How many coding problems are asked? A6: Typically one or two primary coding problems, sometimes with follow-up questions or variations.
