30 Software Engineering Interview Questions You Must Know

Preparing for a software engineering interview can be daunting, but the key is focusing on the right questions. Below, we’ve compiled 30 must-know software engineering interview questions that cover core technical concepts and behavioral insights, ensuring you’re ready to tackle any challenge.

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Core Technical Questions (1-10)

What is the difference between an array and a linked list?
- Array: Fixed size, continuous memory, faster access via index but costly insertions/deletions.
- Linked List: Dynamic size, non-continuous memory, slower access but efficient insertions/deletions.
Explain how garbage collection works in Java.
Java's garbage collector automatically frees memory by identifying and removing objects no longer in use. Techniques include:
- Mark-and-Sweep: Identifies reachable objects, deletes unreachable ones.
- Generational Collection: Separates objects into young, old, and permanent generations to optimize collection.
What’s the time complexity of binary search? Why does it require a sorted array?
- Time Complexity: O(log n) because the search space halves each time.
- Requirement: A sorted array ensures binary division of search space is valid.
How do RESTful APIs work? What makes them stateless?
RESTful APIs use HTTP methods (GET, POST, etc.) to perform operations on resources. They are stateless because the server does not retain client information between requests, improving scalability.
What is a race condition, and how can you prevent it?
A race condition occurs when multiple threads/processes access shared data simultaneously. Prevention methods include:
- Locks
- Mutexes
- Thread-safe programming practices.
Explain the concept of polymorphism in object-oriented programming.
Polymorphism allows objects of different classes to be treated as objects of a common superclass. It enables method overriding (runtime polymorphism) and method overloading (compile-time polymorphism).
What is the difference between a deep copy and a shallow copy in programming?
- Shallow Copy: Copies the top-level elements; references to nested objects remain the same.
- Deep Copy: Copies all nested objects recursively, creating independent copies of all objects.
What are the benefits of using version control systems like Git?
Version control systems allow developers to track changes, collaborate effectively, revert to previous versions, and resolve conflicts between changes made by different developers.
What is the difference between SQL and NoSQL databases?
- SQL: Relational, structured data, uses tables, and supports ACID transactions.
- NoSQL: Non-relational, unstructured data, supports horizontal scaling, and can store various data types (e.g., key-value, document-based).
How does multithreading improve performance in programming?

Multithreading allows multiple threads to run concurrently, utilizing multiple CPU cores, improving performance by handling multiple tasks simultaneously without blocking other tasks.

Algorithms and Data Structures (11-20)

What are the differences between a stack and a queue? When would you use each?

Stack: LIFO (Last In, First Out). Use for undo operations, expression evaluation.
Queue: FIFO (First In, First Out). Use for scheduling, task management.

How do you find the middle of a linked list in one pass?

Use two pointers:

One pointer moves two steps at a time (fast).
The other moves one step (slow).
When fast reaches the end, slow will be at the middle.

Explain the difference between a binary tree and a binary search tree.

Binary Tree: Each node has at most two children, with no specific ordering rules.
Binary Search Tree: A binary tree where left child nodes are less than the parent, and right child nodes are greater.

What is dynamic programming, and how is it different from recursion?

Dynamic programming is a method of solving problems by breaking them down into smaller subproblems, storing their solutions, and avoiding repeated calculations. It differs from recursion, which solves subproblems independently without storing results.

What is the time complexity of the quicksort algorithm?

The average time complexity of quicksort is O(n log n), but in the worst case, it can be O(n^2), typically when the pivot selection is poor.

System Design and Architecture (21-25)

How would you design a URL shortening service like Bitly?

Use a hash function to generate short codes.
Store mappings in a database (key: short code, value: original URL).
Add caching for frequently accessed URLs.
Ensure scalability with database sharding and load balancers.

Explain the CAP theorem and its significance in distributed systems.

The CAP theorem states that in a distributed system, only two of the following three guarantees can be achieved:

Consistency
Availability
Partition Tolerance
Systems must choose two of these properties based on their requirements.

How would you design an e-commerce checkout system?

Components: Payment gateway integration, user authentication, inventory management, order processing.
Ensure scalability with microservices, load balancing, and database replication.

What are the differences between monolithic and microservices architecture?

Monolithic: A single unified application. Harder to scale and maintain as the system grows.
Microservices: Breaks down the system into independent, loosely coupled services. Easier to scale and maintain, but requires more complex management.

How would you ensure high availability in a distributed system?

High availability can be achieved through techniques like:

Replication: Multiple instances of services.
Load balancing: Distributing traffic across multiple servers.
Failover: Automatic switching to a standby server in case of failure.

How to Use These Questions

Start by practicing your answers to the technical questions on a whiteboard or coding platform. For system design and behavioral questions, rehearse by articulating your thought process clearly and concisely. Consider recording yourself to refine your responses.

Good luck!