Write a program to find the first non-repeating character in a string.

Count character frequencies in one pass (hash map or 26-size array), then scan again for the first character with count 1. State O(n) time and O(1) extra space, and be ready to code it live.

Explain the difference between a stack and a queue, with real use cases.

Stack is LIFO (undo operations, function call stack, expression evaluation); queue is FIFO (print jobs, task scheduling, BFS traversal). Give one use case for each without prompting.

What is normalisation in DBMS? Explain up to 3NF.

1NF: atomic values, no repeating groups. 2NF: no partial dependency on part of a composite key. 3NF: no transitive dependency. Use a small student-course table as your example.

How would you design a URL shortener like bit.ly?

Keep it basic but structured: generate a short unique key (hash or counter + base62), store key-to-URL in a database, redirect on lookup. Mention handling collisions and scale briefly.

What is the difference between process-based and thread-based concurrency?

Processes have separate memory and are isolated but costly; threads share memory, are lightweight, but need locks to avoid race conditions. Mention a deadlock example if asked to go deeper.

Explain indexing in databases. When does an index hurt performance?

An index speeds up reads by letting the database find rows without a full scan, but it slows down inserts, updates and deletes because the index must also be updated. Avoid indexing columns that change often.

Reverse a string without using built-in reverse functions.

Use two pointers swapping characters from both ends, or iterate backwards building a new string. State the time complexity and handle edge cases like empty strings.

Walk me through the most complex project on your resume.

Pick the one you know best. Explain the architecture, your exact contribution, the hardest bug you fixed and why you chose that tech stack. Expect them to drill into any term you mention.

Fresher interview prep

TCS Digital interview questions for freshers.

The TCS Digital technical round goes deeper than the Ninja track: expect advanced coding, data structures and algorithms, DBMS, and basic system design, often with follow-ups on your code.

1. Write a program to find the first non-repeating character in a string.
How to answer: Count character frequencies in one pass (hash map or 26-size array), then scan again for the first character with count 1. State O(n) time and O(1) extra space, and be ready to code it live.
2. Explain the difference between a stack and a queue, with real use cases.
How to answer: Stack is LIFO (undo operations, function call stack, expression evaluation); queue is FIFO (print jobs, task scheduling, BFS traversal). Give one use case for each without prompting.
3. What is normalisation in DBMS? Explain up to 3NF.
How to answer: 1NF: atomic values, no repeating groups. 2NF: no partial dependency on part of a composite key. 3NF: no transitive dependency. Use a small student-course table as your example.
4. How would you design a URL shortener like bit.ly?
How to answer: Keep it basic but structured: generate a short unique key (hash or counter + base62), store key-to-URL in a database, redirect on lookup. Mention handling collisions and scale briefly.
5. What is the difference between process-based and thread-based concurrency?
How to answer: Processes have separate memory and are isolated but costly; threads share memory, are lightweight, but need locks to avoid race conditions. Mention a deadlock example if asked to go deeper.
6. Explain indexing in databases. When does an index hurt performance?
How to answer: An index speeds up reads by letting the database find rows without a full scan, but it slows down inserts, updates and deletes because the index must also be updated. Avoid indexing columns that change often.
7. Reverse a string without using built-in reverse functions.
How to answer: Use two pointers swapping characters from both ends, or iterate backwards building a new string. State the time complexity and handle edge cases like empty strings.
8. Walk me through the most complex project on your resume.
How to answer: Pick the one you know best. Explain the architecture, your exact contribution, the hardest bug you fixed and why you chose that tech stack. Expect them to drill into any term you mention.

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TCS Digital interview questions for freshers.

1. Write a program to find the first non-repeating character in a string.

2. Explain the difference between a stack and a queue, with real use cases.

3. What is normalisation in DBMS? Explain up to 3NF.

4. How would you design a URL shortener like bit.ly?

5. What is the difference between process-based and thread-based concurrency?

6. Explain indexing in databases. When does an index hurt performance?

7. Reverse a string without using built-in reverse functions.

8. Walk me through the most complex project on your resume.

Practise these exact questions in a mock interview