Top Technical Interview Questions for Software Engineers

Technical interviews for software engineers test problem-solving skills, coding proficiency, and system design knowledge. To help you prepare, here are the most commonly asked technical questions along with example answers.

Top Technical Interview Questions for Software Engineers

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1. Data Structures and Algorithms Questions

Q1: What is the difference between an array and a linked list?

Answer:

• Array: A fixed-size data structure that allows fast random access.
• Linked List: A dynamic data structure where elements (nodes) are linked using pointers.

📌 Example: Arrays are better for indexed searches, while linked lists are better for dynamic memory allocation and insertion/deletion operations.

Q2: How do you detect a cycle in a linked list?

Answer:

Use Floyd’s Cycle Detection Algorithm (Tortoise and Hare method).

def hasCycle(head):
    slow = fast = head
    while fast and fast.next:
        slow = slow.next
        fast = fast.next.next
        if slow == fast:
            return True
    return False

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2. Object-Oriented Programming (OOP) Questions

Q3: What are the four pillars of OOP?

Answer:

1. Encapsulation – Hiding data using access modifiers.
2. Abstraction – Hiding implementation details, exposing only necessary parts.
3. Inheritance – Allowing one class to inherit properties of another.
4. Polymorphism – Allowing methods to have multiple forms.

Q4: What is the difference between abstract classes and interfaces?

Answer:

Feature	Abstract Class	Interface
Methods	Can have both abstract and concrete methods	Only abstract methods (before Java 8)
Fields	Can have instance variables	Only constants
Inheritance	Can inherit only one class	Can implement multiple interfaces

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3. System Design Questions

Q5: How would you design a URL shortening service like Bit.ly?

Answer:

1. Requirements: Shorten URLs, handle redirections, and support analytics.
2. Components:
   • API Layer for user interactions.
   • Database (SQL/NoSQL) for storing URLs.
   • Hashing Algorithm to generate unique short links.
   • Caching (Redis) for fast access to frequently used links.

Q6: How do you scale a database for millions of users?

Answer:

1. Sharding – Splitting the database across multiple servers.
2. Replication – Duplicating databases to improve read performance.
3. Indexing – Optimizing queries for faster lookups.

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4. Database Questions

Q7: What is normalization in databases?

Answer:

Normalization organizes data to eliminate redundancy and improve efficiency.

📌 Example:

• 1NF: Remove duplicate columns.
• 2NF: Ensure that all non-key attributes depend on the primary key.
• 3NF: Remove transitive dependencies.

Q8: What is the difference between SQL and NoSQL databases?

Answer:

Feature	SQL	NoSQL
Structure	Relational (tables)	Non-relational (key-value, document-based)
Schema	Fixed schema	Dynamic schema
Scalability	Vertical scaling	Horizontal scaling

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5. Programming & Coding Questions

Q9: Write a function to check if a string is a palindrome.

Answer:

def is_palindrome(s):
    return s == s[::-1]
print(is_palindrome("racecar"))  # Output: True

Q10: Find the missing number in an array of size N containing numbers from 1 to N+1.

Answer:

def find_missing_number(arr, n):
    total = (n * (n + 1)) // 2
    return total - sum(arr)
print(find_missing_number([1, 2, 3, 5], 5))  # Output: 4

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6. Cloud & DevOps Questions

Q11: What is CI/CD in DevOps?

Answer:

• CI (Continuous Integration): Developers push code frequently, and automated tests run.
• CD (Continuous Deployment/Delivery): Changes are automatically deployed to production after passing tests.

📌 Example: Tools like Jenkins, GitHub Actions, GitLab CI/CD help automate these processes.

Q12: How does load balancing work?

Answer:

Load balancers distribute traffic across multiple servers to prevent overload and ensure high availability.

📌 Example: Round Robin, Least Connections, and IP Hashing are common load balancing strategies.

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7. Operating System & Networking Questions

Q13: What is the difference between process and thread?

Answer:

Feature	Process	Thread
Definition	An independent executing program	A lightweight subprocess
Memory	Separate memory space	Shares memory with the process
Communication	Uses IPC (Inter-Process Communication)	Communicates easily via shared memory

Q14: What is a deadlock? How do you prevent it?

Answer:

A deadlock occurs when processes wait for resources in a circular chain.

🔹 Prevention Techniques:

• Avoid circular wait by assigning priority to resource allocation.
• Use timeouts to break the deadlock condition.

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8. Cybersecurity & Testing Questions

Q15: What are SQL injection attacks? How do you prevent them?

Answer:

SQL injection is a hacking technique where malicious SQL queries are injected into input fields.

🔹 Prevention:

✔ Use prepared statements instead of raw SQL queries.

✔ Validate and sanitize user input.

cursor.execute("SELECT * FROM users WHERE username = ?", (user_input,))

Q16: What is penetration testing?

Answer:

Penetration testing (pen testing) is an ethical hacking process where security professionals simulate cyberattacks to find vulnerabilities.

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Final Tips for Cracking a Software Engineer Interview

✅ Practice coding daily on LeetCode, CodeSignal, and HackerRank.

✅ Review system design concepts like microservices, caching, and API design.

✅ Understand DevOps tools, CI/CD, and cloud platforms like AWS, GCP, and Azure.

✅ Mock interviews help improve confidence and communication skills.