by, Subhajit Gorai
Date: 22/04/2026

OA Analytics

Find previously asked questions in cs oa, interviews, of everything, be it coding, os, cn, maths, aptitude everything. I want to have idea. search in various sources, google reddit all platforms@Web search

I searched across Reddit, GeeksforGeeks, LeetCode Discuss, placement resources, and recent interview experience posts. One clear pattern emerges:

There is no fixed question bank. Companies keep changing exact questions, but the same concepts and problem families repeat again and again. (Reddit)

Below is a consolidated list of what people repeatedly reported.

1. Coding (Most Important)

Nearly every OA contains 2 coding questions (sometimes 1 easy + 1 medium, sometimes 2 medium).

Most repeated topics:

Arrays

Two Sum variations
Prefix Sum
Sliding Window
Kadane
Rotation
Merge intervals
Frequency counting
Sorting-based problems

Questions commonly seen:

Product Except Self
Trapping Rain Water
Max Subarray
Rotate Array
Merge Intervals

Strings

Frequently asked

Longest substring without repeating
Anagrams
Pattern matching
Encoding/Decoding
Palindrome
String compression

HashMaps

Very common

Questions

Group Anagrams
Top K Frequent
Frequency maps
Pair sums
Duplicate detection

Trees

Extremely common

Questions

Diameter of Binary Tree
Lowest Common Ancestor
BST validation
Level Order Traversal
Good Nodes
Serialize/Deserialize

Amazon interview reports repeatedly mention Diameter variations. (Reddit)

Graphs

Often medium difficulty.

Topics

BFS
DFS
Connected Components
Number of Islands
Rotten Oranges
Shortest Path
Topological Sort

Questions reported

Number of Islands
Rotten Oranges
Grid BFS

(Reddit)

Heap / Priority Queue

Common

Questions

Merge K Sorted Lists
K Closest Points
Top K Frequent
Running Median

Amazon interviews mention Merge K Sorted Lists repeatedly. (LeetCode)

Dynamic Programming

Usually one medium.

Topics

Coin Change
LIS
House Robber
Knapsack
Partition

Microsoft experiences particularly mention DP. (GeeksforGeeks)

Binary Search

Very common.

Questions

Koko Eating Bananas
Search in Rotated Array
Capacity to Ship Packages
First/Last Occurrence

Greedy

Very common in OAs.

Amazon OA reports frequently mention greedy-based problems. (Reddit)

2. OS Questions

These appear in MCQ rounds and interviews.

Most repeated:

Process vs Thread

Expected:

Memory
Context switching
Scheduling
Communication

Deadlock

Know

Coffman conditions
Prevention
Avoidance
Detection
Recovery

Scheduling

FCFS
SJF
Priority
Round Robin
Questions like

Calculate average waiting time.

Virtual Memory

Asked repeatedly.

Know

Paging
Segmentation
TLB
Page Fault
Demand Paging

Synchronization

Questions
Semaphore
Mutex
Monitor
Producer Consumer
Readers Writers
Dining Philosophers

Memory Allocation

Internal fragmentation
External fragmentation
Buddy system

System Calls

Difference
User mode
Kernel mode
Interrupt
Trap

3. DBMS

Repeated almost everywhere.
Normalization
1NF
2NF
3NF
BCNF

SQL

Questions

GROUP BY
HAVING
Window Functions
JOIN
Self Join
Left Join
Indexes

Transactions

ACID
Isolation Levels
Deadlock
Locking

Indexes

B Tree
Hash
Clustered
Non-clustered

4. Computer Networks

Very frequently asked.

TCP vs UDP

HTTP vs HTTPS

OSI Layers

DNS

ARP

Subnetting

Congestion Control

Three Way Handshake

Four Way Termination

Socket Programming basics

REST APIs

Status Codes
GET
POST
PUT
DELETE

5. OOP

Very common.

Questions
Inheritance
Polymorphism
Abstraction
Encapsulation
Virtual Function
Constructor
Destructor
Overloading vs Overriding
Composition vs Inheritance
Interface vs Abstract Class
Diamond Problem
SOLID Principles

6. Mathematics

Many OAs include these.
Probability
Permutations
Combinations
Modular Arithmetic
GCD
LCM
Prime
Logarithms
Recurrence
Basic Calculus (rare)
Matrix operations
Bit Manipulation

7. Aptitude

Repeated topics
Time and Work
Speed Distance
Pipes
Probability
Profit Loss
Simple Interest
Compound Interest
Ratios
Number Systems
Logical Reasoning
Blood Relations
Seating Arrangement
Coding Decoding
Series
Syllogisms

8. Behavioral Questions

Amazon especially.

Examples
Tell me about a challenge.
Tell me about a conflict.
Failure.
Leadership.
Innovation.
Deadline.
Ownership.
Difficult teammate.
Disagreement.
These are based on Amazon Leadership Principles. (Reddit)

9. Resume-Based Questions

Every interviewer asks things like
Explain your project.
Why did you choose this architecture?
Biggest challenge?
How would you scale it?
How is authentication handled?
Database choice?
Trade-offs?

Since you've built projects like Flask applications and worked with embeddings, expect deep follow-up questions on implementation details rather than just features.

10. System Design (Sometimes for Interns, Often for SDE-2)

Examples

Design TinyURL
Design Parking Lot
Design Chat App
Design Rate Limiter
Design Cache
Design URL Shortener
LLD examples
Chess
LRU Cache
Elevator
Snake & Ladder
Library Management

Amazon SDE-II experiences commonly report LLD/HLD after the OA. (LeetCode)

11. OA Pattern (Most Common)

Most companies follow roughly:

txt
Resume
      ↓
Online Assessment

2 Coding Problems

+ Aptitude (sometimes)

+ CS MCQs

+ Work Simulation (Amazon)

+ Behavioral
      ↓

Technical Interview

DSA

OS

CN

DBMS

Projects

Resume
      ↓

HR
Resume
      ↓
Online Assessment

2 Coding Problems

+ Aptitude (sometimes)

+ CS MCQs

+ Work Simulation (Amazon)

+ Behavioral
      ↓

Technical Interview

DSA

OS

CN

DBMS

Projects

Resume
      ↓

HR

(Placement Papers)

12. What Reddit Analysis Shows

A community analysis of around 300 publicly shared interview questions found:

71% came from Online Assessments.
The most common coding tasks were practical data manipulation rather than obscure dynamic programming.
Amazon appeared most frequently among shared experiences, followed by Uber, TikTok, Microsoft, Snowflake, Google, Salesforce, Stripe, and Meta. (Reddit)

High-Yield Preparation Order

If you want the best return on your preparation time, prioritize:

Arrays & Hash Maps
Strings & Sliding Window
Binary Search
Trees & BST
Graphs (BFS/DFS)
Heaps
Greedy
Dynamic Programming
OS fundamentals
DBMS (SQL + normalization + ACID)
Computer Networks (TCP/IP, HTTP, DNS)
OOP & SOLID
Aptitude & probability
Behavioral stories (STAR format)

If you're targeting product companies (Google, Microsoft, Amazon, Atlassian, Adobe, Salesforce, Walmart, Flipkart, etc.), this list covers the overwhelming majority of topics reported across recent OAs and technical interviews.

@Web search exact questions can you find in cs theory / apti?

Yes. I found actual questions reported by candidates. While companies rarely reuse the exact same MCQs, the following questions (or extremely close variants) appear repeatedly across interview experiences.

Operating Systems

1. Process vs Thread ⭐⭐⭐⭐⭐

Explain the difference between a process and a thread.

Follow-up:

Which has its own address space?
Which is cheaper to create?
Which shares memory?
Context switching cost?

Asked in:

Infosys
Oracle
Perfios
OFSS
Numerous interview reports (GeeksforGeeks)

2. What is a deadlock?

Then

Four Coffman conditions
Prevention
Avoidance
Detection
Recovery

3. Difference between Mutex and Semaphore

Classic interview question.

4. What is a context switch?

What gets saved?

PCB?

Registers?

Program Counter?

5. CPU Scheduling

Given

P1  BT=8
P2  BT=4
P3  BT=9
P4  BT=5

Find

Waiting Time
Turnaround Time

using

FCFS
SJF
RR

Very common MCQ.

6. Virtual Memory

Questions like

Why do we need virtual memory?

What is paging?

Difference between paging and segmentation?

7. Page Replacement

MCQ

FIFO

Reference String

7 0 1 2 0 3 0 4

How many page faults?

This exact pattern is common. (FACE Prep)

DBMS

1. ACID Properties ⭐⭐⭐⭐⭐

Explain

Atomicity

Consistency

Isolation

Durability

2. Normalization

Very frequently

Is this table in 2NF?

3NF?

BCNF?

Convert this table into 3NF.

Appears almost everywhere. (GeeksforGeeks)

3. SQL Queries

Very common.

Examples

Find second highest salary.

Nth highest salary.

Employee

Department

INNER JOIN

LEFT JOIN

GROUP BY

HAVING

Window Functions

ROW_NUMBER()

RANK()

4. Indexes

Difference

B Tree

Hash

Clustered

Non-clustered

5. Keys

Difference between

Primary

Candidate

Alternate

Composite

Foreign

6. Transactions

Dirty Read

Non Repeatable Read

Phantom Read

Computer Networks

1. TCP vs UDP ⭐⭐⭐⭐⭐

Almost every report mentions this. (GeeksforGeeks)

2. Three Way Handshake

Explain

SYN

SYN ACK

ACK

3. Four Way Connection Termination

FIN

ACK

4. HTTP vs HTTPS

5. DNS

How google.com is resolved.

6. Socket vs Port

Oracle interview specifically asked

Difference between port and socket. (GeeksforGeeks)

7. OSI Model

Typical MCQ

Which layer performs routing?

A)

Transport

B)

Network

C)

Application

D)

Data Link

OOP

Asked everywhere.

Examples

Difference

Overloading

vs

Overriding

Interface

vs

Abstract Class

Composition

vs

Inheritance

Virtual Function?

What is polymorphism?

Diamond Problem?

Aptitude

Quant

Repeated topics

Time & Work

A can finish in 12 days

B in 18 days

Together?

Probability

Two dice

Probability sum = 8

Permutation

How many ways

MISSISSIPPI

Profit Loss

20% gain

10% loss

Net?

Speed Distance

Train crosses pole

Bridge

Platform

Pipes

Classic.

Ratios

SI CI

Ages

Logical Reasoning

Very common.

Blood Relation

Coding Decoding

APPLE

→

CRRNG?

Seating Arrangement

Syllogisms

All dogs are animals

Some animals...

Number Series

2 6 12 20 30 ?

Technical Aptitude

These surprise many students.

Example

What is complexity?

for(i=1;i<n;i++)
   for(j=1;j<n;j++)

Output of C code

Stack trace

Binary tree traversal

Queue operation

Binary Search iterations

These are almost identical to technical aptitude rounds used by TCS, Infosys, Capgemini, etc. (FACE Prep)

Real Questions Reported by Candidates

Some interview reports include exact questions:

Perfios

Process vs Thread
TCP vs UDP
Reverse Linked List
Sort 0s and 1s
Level Order Traversal
Design a database and write SQL queries. (GeeksforGeeks)

Oracle

Difference between Port and Socket
Interface vs Abstract Class
Design Chess using OOP
AVL Trees
Red-Black Trees
Maximum Sum Path in Binary Tree
Equilibrium Index (GeeksforGeeks)

Infosys

Four pillars of OOP
Types of Keys
Virtual keyword
File handling
Difference between C and C++
SQL joins
Identify Normal Form (GeeksforGeeks)

Citrix OA

XOR-based bit manipulation problem
Technical MCQs from DSA, DBMS, CN, OS
Aptitude questions (GeeksforGeeks)

Anchanto

Coin Change
Weighted Job Scheduling
SQL queries
Technical MCQs on C/C++, Java, DBMS, OS, CN (GeeksforGeeks)

Best Sources for Hundreds of Real Questions

These consistently contain actual interview questions shared by candidates:

GeeksforGeeks Interview Experiences
LeetCode Discuss – Interview Experiences
GeeksforGeeks Core CS Interview Course
StudyBench CS Core Placement Guide
Reddit communities such as r/developersIndia, r/Btechtards, r/LeetcodeDesi, and r/PlacementsPrep, where candidates often post detailed OA and interview experiences. (Reddit)

If you're preparing for campus placements or SDE internships, I can also compile a "Top 300 Most Repeated CS Theory Questions" (OS + DBMS + CN + OOP + Aptitude), distilled from hundreds of interview experiences into a single revision document. It would focus only on the questions that recur most often.

@Web search Focus one by one then. first go for OS, find all actually asked questions you can get. shoud be asked in oa/interview. its important.

I went through interview experiences (Oracle, Cisco, Google, Nvidia, campus placements), Reddit discussions, and OS interview question compilations. A strong pattern emerged:

Around 80–90% of OS interview questions come from the same ~40 concepts. Companies change the wording and depth, but the underlying questions repeat. (GeeksforGeeks)

Below is a consolidated list of actual questions that candidates reported being asked in OAs and technical interviews.

Tier 1 (Asked Everywhere) ⭐⭐⭐⭐⭐

These are the highest-frequency OS questions.

Process & Thread

These appear in nearly every company.

Actual questions:

What is a process?
What is a thread?
Difference between process and thread.
Why are threads called lightweight processes?
Does every process have at least one thread?
What resources are shared between threads?
What resources are NOT shared?
When should you use processes instead of threads?
Which context switch is cheaper, process or thread? Why?
Can one thread crash another?
If one thread crashes, what happens to the process?
User-level threads vs kernel-level threads.
How are threads scheduled?

Interview reports:

Cisco
Oracle
Nvidia
Google prep guides
Infosys
Numerous campus interviews (Reddit)

Process Lifecycle

Questions:

Draw process state diagram.
Difference between Ready and Waiting.
Can a process go directly from Waiting to Running?
Zombie process?
Orphan process?
Process Control Block (PCB)?
What information is stored in PCB?
What happens during fork()?
Difference between fork() and exec().

Context Switching

Repeated everywhere.

Questions:

What is context switching?
Why is it expensive?
What is saved during context switch?
Does switching threads require kernel involvement?
Hardware role in context switching?
What triggers a context switch?
Voluntary vs involuntary context switch.

Tier 2 — CPU Scheduling ⭐⭐⭐⭐⭐

Extremely common.

Questions:

FCFS
SJF
SRTF
Round Robin
Priority Scheduling
Multilevel Queue
Multilevel Feedback Queue

Calculation questions:

P1 BT=8 AT=0
P2 BT=4 AT=1
P3 BT=9 AT=2
P4 BT=5 AT=3

Find

Waiting Time

Turnaround Time

Completion Time

MCQs often ask:

Which scheduling algorithm minimizes average waiting time?
Which causes starvation?
Which is preemptive?
Which is used in time-sharing?
Effect of quantum size in Round Robin.

Tier 3 — Deadlock ⭐⭐⭐⭐⭐

One of the most repeated interview topics.

Questions:

What is deadlock?
Give a real-life example.
Four Coffman conditions.
Can deadlock occur with one process?
Deadlock prevention.
Deadlock avoidance.
Detection.
Recovery.
Banker's Algorithm.
Safe state.
Unsafe state.
Resource Allocation Graph.
Wait-for Graph.
Difference between deadlock and starvation.
Difference between deadlock and livelock.

Tier 4 — Synchronization ⭐⭐⭐⭐⭐

Actual questions:

Race condition.
Critical section.
Why do race conditions occur?
Mutex vs Semaphore.
Binary semaphore vs mutex.
Counting semaphore.
Spinlock.
Monitor.
Condition Variable.
Atomic operation.
Busy waiting.
Test-and-Set instruction.
Compare-and-Swap.

Classic problems:

Producer Consumer
Readers Writers
Dining Philosophers
Sleeping Barber

Interviewers often ask how you would solve one of these using semaphores or mutexes.

Tier 5 — Memory Management ⭐⭐⭐⭐⭐

Repeated in almost every interview.

Questions:

What is virtual memory?
Why is virtual memory needed?
Paging.
Segmentation.
Difference between paging and segmentation.
Logical vs physical address.
Page table.
TLB.
TLB hit ratio.
Demand paging.
Page fault.
Thrashing.
Working set.
Internal fragmentation.
External fragmentation.
Buddy allocator.

Tier 6 — Page Replacement ⭐⭐⭐⭐

MCQs frequently use numerical problems.

Typical question:

Frames = 3

Reference String

7 0 1 2 0 3 0 4 2 3

FIFO

How many page faults?

Algorithms:

FIFO
LRU
Optimal
Clock

Also:

Bélády's Anomaly.
Which algorithm is stack-based?
Why doesn't LRU exhibit Bélády's anomaly?

Tier 7 — System Calls ⭐⭐⭐⭐

Questions:

What is a system call?
Examples of system calls.
User mode vs kernel mode.
Interrupt vs trap vs exception.
How does read() work internally?
What happens after a system call?
Why can't user programs directly access hardware?

Tier 8 — IPC (Inter-Process Communication) ⭐⭐⭐⭐

Questions:

Why is IPC needed?
Shared Memory.
Message Queue.
Pipe.
Named Pipe.
Socket.
Signal.
Memory-mapped files.

Comparison questions:

Pipe vs Socket.
Shared Memory vs Message Passing.

Tier 9 — File Systems ⭐⭐⭐⭐

Questions:

What is an inode?
Hard link vs soft link.
Directory structure.
Journaling.
FAT vs NTFS vs ext4.
Mounting.
File descriptor.
Buffer cache.

Tier 10 — Disk Scheduling ⭐⭐⭐

Questions:

FCFS
SSTF
SCAN
LOOK
C-SCAN
C-LOOK

Calculation questions are common.

Tier 11 — Miscellaneous Concepts ⭐⭐⭐

Questions include:

Multiprogramming vs multitasking.
Time-sharing.
Batch OS.
Real-time OS (hard vs soft).
Monolithic kernel vs microkernel.
Multiprocessing vs multithreading.
SMP vs AMP.
NUMA basics.
Cache affinity / CPU affinity (more common in systems roles). (GeeksforGeeks)

Coding / Practical OS Questions

Occasionally asked in interviews:

Implement Producer–Consumer.
Reader–Writer synchronization.
Implement Semaphore.
Implement LRU Cache.
Design Thread Pool.
Explain fork() + exec() execution.
Write code demonstrating deadlock and fix it.

Cisco interview reports also mention implementing an LRU cache live, alongside OS questions on mutexes, semaphores, deadlocks, and process vs. thread. (Reddit)

Questions Specifically Reported in Company Interviews

Oracle

Process vs Thread
Context Switching
Deadlock
Scheduling
Virtual Memory (Reddit)

Cisco

Mutex vs Semaphore
Process vs Thread
Deadlock
OS MCQs in OA (Reddit)

Google (prep guidance)

Processes
Threads
Locks
Mutexes
Semaphores
Monitors
Deadlocks
Context switching
Scheduling (Reddit)

NVIDIA

Scheduling
Virtual Memory
Paging
Deadlocks
Synchronization
Cache
Interrupts
Context Switching (Reddit)

If you only study 30 OS questions...

These cover the overwhelming majority of what appears in interviews:

Process vs Thread
PCB
Process States
Context Switch
User vs Kernel Threads
FCFS
SJF
Round Robin
Priority Scheduling
Waiting & Turnaround Time
Deadlock
Coffman Conditions
Banker's Algorithm
Mutex vs Semaphore
Race Condition
Critical Section
Producer–Consumer
Readers–Writers
Virtual Memory
Paging
Segmentation
Page Fault
TLB
FIFO vs LRU vs Optimal
Thrashing
System Calls
User Mode vs Kernel Mode
IPC (Pipes, Shared Memory, Message Queues)
Inodes & Hard vs Soft Links
Monolithic vs Microkernel

This is the "high-yield" OS set that repeatedly appears across campus OAs, SDE interviews, and systems-focused interviews according to recent interview experiences and preparation resources. (GeeksforGeeks)

@Web search Now gather for DBMS, again, focus that things should be actually asked before.

After looking through candidate interview experiences, OA reports, GeeksforGeeks interview archives, and Reddit placement discussions, one thing is very clear:

DBMS interviews are much more repetitive than DSA. Roughly 80% of questions come from the same concepts, and many companies ask nearly identical questions. (GeeksforGeeks)

Below is a list of questions that have actually been reported by candidates, organized by frequency.

Tier 1 (Asked Almost Everywhere) ⭐⭐⭐⭐⭐

These should be considered mandatory.

1. Normalization

Probably the #1 DBMS interview topic.

Actual questions:

What is normalization?
Why do we normalize?
Explain 1NF.
Explain 2NF.
Explain 3NF.
Explain BCNF.
Difference between 3NF and BCNF.
Given a table, normalize it to 3NF.
What anomalies does normalization remove?
When should you denormalize?

Interview reports repeatedly mention interviewers asking candidates to identify the normal form of a table or normalize a schema. (GeeksforGeeks)

2. ACID Properties

Very frequently asked.

Questions

What is a transaction?
Explain ACID.
Why is Atomicity important?
Difference between Consistency and Isolation.
Give a real-life example of Atomicity.
What happens if Durability fails?

Recent TCS interview experiences specifically mention ACID as one of the first DBMS questions. (Reddit)

3. Keys

Questions

Primary Key
Candidate Key
Super Key
Alternate Key
Composite Key
Foreign Key

Common follow-ups

Can Primary Key be NULL?
Can Foreign Key be NULL?
Difference between Candidate and Primary Key.
Difference between Primary Key and Unique Key.

4. SQL Queries

Probably every interview.

Repeated questions

Second Highest Salary

sql
Find the second highest salary.
Find the second highest salary.

Nth Highest Salary

Duplicate Rows

sql
Find duplicate rows.
Find duplicate rows.

Employees earning more than manager

Customers without orders

Department-wise highest salary

Average salary department-wise

Delete duplicate rows

Consecutive records

Running total

Window Functions

Questions

ROW_NUMBER()
RANK()
DENSE_RANK()

The "second highest salary" problem is one of the most frequently reported SQL interview questions. (GeeksforGeeks)

Tier 2 (Very Frequently Asked) ⭐⭐⭐⭐

JOINs

Questions

Difference between

INNER JOIN
LEFT JOIN
RIGHT JOIN
FULL OUTER JOIN
CROSS JOIN
SELF JOIN

Interviewers often draw two tables and ask you to sketch the output.

GROUP BY

Questions

Difference between

sql
WHERE

HAVING

GROUP BY
WHERE

HAVING

GROUP BY

Typical question

sql
Find departments having more than five employees.
Find departments having more than five employees.

DELETE vs TRUNCATE vs DROP

One of the most repeated interview questions.

Expected comparison

Rollback?
Logging?
Removes structure?
Removes data?
Speed?

Recent TCS interview reports specifically mention DELETE vs TRUNCATE being asked. (Reddit)

UNION vs UNION ALL

Questions

Difference?

Duplicates?

Performance?

EXISTS vs IN

Frequently reported.

CHAR vs VARCHAR

Very common for Oracle/MySQL roles. (GeeksforGeeks)

Tier 3 (Transactions & Concurrency) ⭐⭐⭐⭐

Concurrency Control

Questions

Why is concurrency needed?
Lost Update
Dirty Read
Phantom Read
Non-repeatable Read

Isolation Levels

Questions

Explain

Read Uncommitted
Read Committed
Repeatable Read
Serializable

Follow-up

Which anomalies does each prevent?

Locks

Questions

Shared Lock
Exclusive Lock
Intention Lock
Lock Granularity

Deadlock

Questions

Can databases have deadlocks?

How are they detected?

How are they prevented?

Tier 4 (Indexing) ⭐⭐⭐⭐

One of the favorite interview topics.

Questions

What is an Index?
Why use Index?
Why not create indexes everywhere?
Clustered Index
Non-clustered Index
Composite Index
Covering Index

Follow-up

When does an index hurt performance?

B+ Tree

Very common.

Questions

Why B+ Tree?
Why not Binary Search Tree?
Why not Hash Table?
Why do databases prefer B+ Trees?

Tier 5 (ER Model) ⭐⭐⭐⭐

Questions

Entity
Attribute
Relationship
Weak Entity
Cardinality
Participation
ER Diagram

Often

Draw ER diagram for Library.

Design Student-Course database.

Tier 6 (Database Design) ⭐⭐⭐

Questions

Design

Banking database
Hospital database
Library
Food delivery
College Management
Airline Reservation

Interviewers then ask

Primary keys?
Foreign keys?
Normalization?
Relationships?

Tier 7 (Functions & SQL Internals) ⭐⭐⭐

Questions

Stored Procedure
Trigger
View
Materialized View
Cursor
Function

Common follow-up

Difference between View and Materialized View.

Tier 8 (Architecture) ⭐⭐⭐

Questions

DBMS vs RDBMS
Schema vs Instance
Logical vs Physical Schema
Data Independence
Three Schema Architecture

Tier 9 (Unexpected but Reported)

These appear less often but are worth knowing.

Query Execution

Real question reported

How does a SQL database engine execute a query?

One interviewee shared being asked to explain what happens internally after a SQL query is issued. (Reddit)

Query Optimization

Questions

Why is one query faster?
Explain execution plan.
Full Table Scan.
Index Scan.

CAP Theorem

Occasionally asked for backend roles.

SQL Coding Questions Reported Repeatedly

These problems appear again and again:

Problem	Frequency
Second Highest Salary	⭐⭐⭐⭐⭐
Nth Highest Salary	⭐⭐⭐⭐⭐
Duplicate Rows	⭐⭐⭐⭐
Department-wise Highest Salary	⭐⭐⭐⭐
Employee > Manager Salary	⭐⭐⭐⭐
Customers without Orders	⭐⭐⭐⭐
Top N Salaries	⭐⭐⭐⭐
Consecutive Dates	⭐⭐⭐
Running Total	⭐⭐⭐
Dense Rank	⭐⭐⭐⭐
Find Missing Records	⭐⭐⭐
Remove Duplicates	⭐⭐⭐⭐

These are common enough that many interview preparation sites include them verbatim. (GeeksforGeeks)

Questions Specifically Reported by Companies

TCS

Reported questions:

DELETE vs TRUNCATE
Normalization
Where would you use normalization?
ACID Properties
SQL queries from projects (Reddit)

Infosys

Repeated reports mention:

SQL queries
Normal Forms
Joins
Keys
DBMS basics (Reddit)

Oracle

Reported questions include:

Indexes
Joins
Normalization
Transactions
SQL query writing (GeeksforGeeks)

If You Only Study 30 DBMS Questions

These provide excellent coverage for campus placements and SDE interviews:

DBMS vs RDBMS
Schema vs Instance
Three-schema architecture
Primary Key
Candidate Key
Foreign Key
Composite Key
Super Key
Functional Dependency
1NF
2NF
3NF
BCNF
Denormalization
ACID Properties
Transactions
Isolation Levels
Deadlock in DBMS
Indexes
Clustered vs Non-clustered Index
B+ Tree
INNER/LEFT/RIGHT/FULL JOIN
GROUP BY vs HAVING
DELETE vs TRUNCATE vs DROP
UNION vs UNION ALL
EXISTS vs IN
Second Highest Salary (SQL)
Window Functions (ROW_NUMBER, RANK, DENSE_RANK)
Views vs Materialized Views
Stored Procedures vs Triggers

This set aligns closely with what candidates consistently report across OAs and technical interviews and will prepare you for the majority of DBMS discussions in placements.

@Web search OOP now

After reviewing recent interview experiences, campus placement reports, Reddit discussions, and OOP interview compilations, OOP has the smallest and most repetitive question pool among the CS core subjects.

Unlike OS or DBMS, interviewers usually don't ask obscure OOP theory. They ask basic concepts, followed by design trade-offs and small coding scenarios. (GeeksforGeeks)

Tier 1 — Asked in Almost Every Interview ⭐⭐⭐⭐⭐

These are the questions that appear repeatedly across Infosys, Oracle, SAP, Goldman Sachs, OFSS, and many campus interviews.

1. What is OOP?

Usually followed by:

Why OOP?
Advantages over procedural programming?
Real-world example?
Why Java/C++ are object-oriented?

2. Four Pillars of OOP ⭐⭐⭐⭐⭐

Probably the most asked OOP question.

Interviewers ask:

Explain Encapsulation.
Explain Abstraction.
Explain Inheritance.
Explain Polymorphism.

Then immediately ask

Give a real-life example.

Give a coding example.

This is reported in multiple SAP Labs and AppViewX interview experiences. (GeeksforGeeks)

Encapsulation

Actual follow-ups

Why use private members?
Can encapsulation exist without classes?
Difference between encapsulation and data hiding?
Why getters/setters?

Abstraction

Questions

What is abstraction?
Why abstract?
Abstract class vs abstraction.
Can abstraction exist without abstract class?

Inheritance

Questions

Why inheritance?
Types of inheritance.
Why Java doesn't support multiple inheritance through classes?
Diamond Problem.
Method inheritance.

Polymorphism

Questions

Compile-time polymorphism.
Runtime polymorphism.
Function overloading.
Function overriding.
Dynamic dispatch.
Virtual function.

Tier 2 — Class Relationships ⭐⭐⭐⭐⭐

Abstract Class vs Interface

Probably the single most repeated comparison question.

Interviewers ask

Difference?
When to use interface?
When to use abstract class?
Can interface have methods?
Can interface have variables?
Multiple inheritance?

This appears in Infosys and SAP interview reports. (Reddit)

Composition vs Inheritance

Repeated especially in product companies.

Questions

"Has-a" vs "Is-a"
Which is better?
When should you avoid inheritance?

Association

Questions

Difference between

Association
Aggregation
Composition

Almost always accompanied by a UML-style example.

Tier 3 — Overloading & Overriding ⭐⭐⭐⭐⭐

Another favorite.

Questions

Difference between

Method Overloading
Method Overriding

Follow-ups

Return type?
Access modifier?
Static methods?
Private methods?
Constructor overloading?
Operator overloading?

Tier 4 — Constructors ⭐⭐⭐⭐

Questions

Default constructor
Parameterized constructor
Copy constructor (C++)
Constructor overloading
Constructor chaining
Destructor (C++)
Why constructor cannot be virtual?

Tier 5 — Access Specifiers ⭐⭐⭐⭐

Frequently reported in SAP interviews.

Questions

Difference between

Public
Private
Protected

Follow-ups

Can private methods be inherited?
Can protected members be accessed outside package?
Which access modifier is default?

SAP Labs interviewers specifically asked multiple variations involving C++ access specifiers. (GeeksforGeeks)

Tier 6 — Static vs Dynamic ⭐⭐⭐⭐

Questions

Static variable
Static method
Static binding
Dynamic binding
Early binding
Late binding

Tier 7 — Virtual Functions (C++) ⭐⭐⭐⭐

Questions

Why virtual?
Vtable?
Runtime polymorphism?
Pure virtual function?
Abstract class?

Tier 8 — Memory & Object Lifetime ⭐⭐⭐

Questions

Stack vs Heap objects
new vs malloc
delete vs free
Constructor call order
Destructor call order

Mostly C++ interviews.

Tier 9 — SOLID Principles ⭐⭐⭐

Increasingly common in backend interviews.

Questions

Explain

Single Responsibility
Open Closed
Liskov Substitution
Interface Segregation
Dependency Inversion

Sometimes

Give real example.

Tier 10 — Scenario-Based Questions ⭐⭐⭐⭐

Instead of theory, interviewers often ask

Design a Library

Classes?

Inheritance?

Composition?

Design Parking Lot

Design ATM

Design Vending Machine

Oracle interview reports mention explaining a vending machine interface, focusing on OOP design rather than implementation. (GeeksforGeeks)

Design Chess

Frequently reported.

Design Student Management

Design Online Shopping Cart

Design Bank Account

Tier 11 — Small Coding Questions

Sometimes interviewers ask you to write code.

Examples

Implement

cpp
Animal

Dog

Cat
Animal

Dog

Cat

Demonstrate

Inheritance
Overriding
Runtime polymorphism

Implement

cpp
Shape

Circle

Rectangle
Shape

Circle

Rectangle

Implement

cpp
Employee

Manager
Employee

Manager

Implement

cpp
Vehicle

Bike

Car
Vehicle

Bike

Car

MCQs Frequently Seen in OAs

Examples

Which pillar hides implementation?

A) Inheritance

B) Encapsulation

C) Abstraction

D) Polymorphism

Which supports runtime polymorphism?

A) Overloading

B) Overriding

C) Templates

D) Constructor

Java supports multiple inheritance through?

A) Classes

B) Interface

C) Objects

D) Packages

Which relationship is "Has-A"?

Which keyword prevents inheritance?

Which member cannot be overridden?

Questions Specifically Reported by Companies

Infosys

Reported questions

Abstract class vs Interface
Inheritance
Project discussion using OOP concepts (Reddit)

SAP Labs

Reported

Access specifiers
Abstract class
Interface
OOP fundamentals (GeeksforGeeks)

AppViewX

Reported

Four pillars of OOP
Real-life examples
Instagram feature design using OOP (GeeksforGeeks)

OFSS

Reported

Basic OOP concepts in OA MCQs
Output-based OOP questions
Language-specific OOP fundamentals (GeeksforGeeks)

Goldman Sachs

Reported

OA MCQs on OOP fundamentals alongside OS and DSA. (GeeksforGeeks)

If You Only Study 25 OOP Questions

These cover the overwhelming majority of interview questions:

What is OOP?
Advantages of OOP
Object vs Class
Encapsulation
Abstraction
Inheritance
Polymorphism
Data Hiding vs Encapsulation
Abstract Class vs Interface
Method Overloading vs Overriding
Compile-time vs Runtime Polymorphism
Association vs Aggregation vs Composition
Composition vs Inheritance
Access Specifiers
Static vs Dynamic Binding
Virtual Functions
Constructors
Destructors
Copy Constructor (C++)
Diamond Problem
Multiple Inheritance
SOLID Principles (basics)
Design a Parking Lot/Library/ATM using OOP
UML basics (class relationships)
Write a small inheritance hierarchy (e.g., Shape, Vehicle, Employee) demonstrating overriding and polymorphism.

A notable trend

One recurring theme in recent interview experiences is that many interviewers move beyond definitions. After asking "What is encapsulation?" or "Interface vs abstract class?", they often follow with a prompt like:

"Design a small system (ATM, Parking Lot, Vending Machine, Library) and explain why you chose inheritance, composition, or interfaces."

Being able to apply OOP concepts in a simple design discussion is often more valuable than memorizing definitions. (Reddit)

@Web search Computer Networks now

After searching through actual interview experiences (Cisco, TCS, network engineer roles, SDE interviews), Reddit discussions, and CN interview archives, Computer Networks turns out to be one of the most standardized CS subjects.

Most interviews repeatedly ask the same 30–40 networking questions. The wording changes, but the concepts are remarkably consistent. (GeeksforGeeks)

Tier 1 (Asked in Almost Every Interview) ⭐⭐⭐⭐⭐

1. OSI Model

This is the most frequently asked CN question.

Actual questions:

Explain the OSI Model.
Explain each layer.
Why do we need layers?
Which layer does routing happen in?
Which layer handles encryption?
Which layer performs error detection?
Which layer is responsible for reliable communication?
Give examples of protocols at each layer.
What data unit (PDU) exists at each layer?
- Bits
- Frames
- Packets
- Segments

Very common follow-up:

"What happens at every OSI layer when you open www.google.com?"

This exact question appears in Cisco interviews and is recommended by interviewers on Reddit. (GeeksforGeeks)

2. TCP vs UDP ⭐⭐⭐⭐⭐

Probably the second most asked question.

Actual questions

Difference between TCP and UDP.
Which is faster?
Why is TCP reliable?
Why is UDP faster?
Why does video streaming use UDP?
Why does HTTP use TCP?
Can UDP be made reliable?
Which header is larger?
Which consumes more bandwidth?

Interviewers almost always ask:

"When would you choose UDP over TCP?"

Appears in Cisco, TCS, and many placement interviews. (GeeksforGeeks)

3. Three-Way Handshake ⭐⭐⭐⭐⭐

Questions

Explain SYN.
Explain SYN-ACK.
Explain ACK.
Why are three steps needed?
Why not two?
Why not four?
What sequence numbers are used for?

Follow-up

What is connection establishment?
What happens if ACK is lost?

4. Four-Way Connection Termination

Questions

Why four packets?
Why not three?
TIME_WAIT?
FIN_WAIT?
CLOSE_WAIT?

5. What happens when you type a URL?

This is one of the most common end-to-end questions.

Interviewers ask:

Explain everything after typing:

text
https://www.google.com
https://www.google.com

Expected flow

Browser cache
DNS lookup
ARP (if needed)
TCP handshake
TLS handshake
HTTP request
Routing
Response
Rendering

Cisco interview experiences explicitly report this question. (GeeksforGeeks)

Tier 2 (Very Frequently Asked) ⭐⭐⭐⭐

6. DNS

Questions

What is DNS?
How does DNS work?
Recursive vs iterative lookup.
What is DNS cache?
Root server?
TLD server?
Authoritative server?

7. HTTP vs HTTPS

Questions

Difference?

Encryption?

SSL?

TLS?

Certificates?

Port numbers?

8. IP Address

Questions

Difference between

IPv4

IPv6

Private IP

Public IP

Loopback

Broadcast

9. Subnetting

Extremely common in Cisco/network-oriented roles.

Questions

Why subnet?
CIDR
Calculate network address
Calculate broadcast address
Number of hosts

Cisco interview reports specifically mention subnetting and supernetting. (GeeksforGeeks)

10. Routers vs Switches vs Hubs

Questions

Difference

Hub

Switch

Router

Bridge

Gateway

Repeats across network engineering interviews. (GeeksforGeeks)

Tier 3 (Protocols) ⭐⭐⭐⭐

ARP

Questions

Why ARP?
ARP Request
ARP Reply
ARP Cache

ICMP

Questions

What is ICMP?
How does ping work?
Does ping use TCP?
Does ping use UDP?

DHCP

Questions

What is DHCP?
Why DHCP?
DHCP Discover
Offer
Request
ACK

Cisco interview reports mention explaining DHCP in detail. (GeeksforGeeks)

NAT

Questions

Why NAT?
Advantages
Private IP to Public IP
PAT

FTP

Questions

Difference

Active

Passive

SMTP

POP3

IMAP

Frequently asked in service-based companies.

Tier 4 (Routing) ⭐⭐⭐⭐

Questions

Routing
Static Routing
Dynamic Routing
Distance Vector
Link State
RIP
OSPF

Follow-up

How does a router decide where to send packets?

Tier 5 (Error & Flow Control) ⭐⭐⭐⭐

Questions

Flow Control
Congestion Control
Sliding Window
Stop-and-Wait
Go-Back-N
Selective Repeat

Cisco interview reports specifically mention Go-Back-N. (GeeksforGeeks)

Tier 6 (Data Link Layer) ⭐⭐⭐

Questions

MAC Address
Frame
CRC
Error Detection
Error Correction

Tier 7 (Application Layer) ⭐⭐⭐

Questions

HTTP

HTTPS

FTP

SMTP

POP3

IMAP

DNS

DHCP

SSH

Telnet

SNMP

Tier 8 (Practical Questions) ⭐⭐⭐

Interviewers increasingly ask practical networking questions.

Examples

What does ping do?
traceroute vs ping
Why ping works even if HTTP fails?
How does Wi-Fi work?
Why can't two devices have the same IP?
Why can't two devices have the same MAC?

Cisco manager interviews specifically asked "How does Wi-Fi work in your home?" (GeeksforGeeks)

MCQs Frequently Seen in OAs

Examples

Which protocol is connection-oriented?

A TCP

B UDP

C IP

D ICMP

Which layer performs routing?

A Transport

B Network

C Data Link

D Session

Which protocol resolves IP to MAC?

A DNS

B DHCP

C ARP

D ICMP

Default HTTP port?

HTTPS?

443

Which protocol is used by ping?

ICMP

Which protocol guarantees ordered delivery?

TCP

Which protocol uses sequence numbers?

TCP

Questions Specifically Reported by Companies

Cisco

Reported questions

OSI model
TCP vs UDP
HTTP vs HTTPS
Routing
Switching
Frame vs Packet
Data Link Layer
Physical Layer
DHCP
Subnetting
Go-Back-N
Explain what happens after typing a URL. (GeeksforGeeks)

TCS

Reported questions

OSI layers
Ping command
Basic networking concepts
Transport layer responsibilities
TCP vs UDP. (Reddit)

Freshers / SDE Interviews

Candidates repeatedly report being asked:

OSI
TCP/IP
TCP vs UDP
DNS
Three-way handshake
"Explain what happens when you enter a URL."
Ping
Traceroute
Routers vs Switches. (Reddit)

If You Only Study 30 CN Questions

These cover the vast majority of networking interviews:

OSI Model
TCP/IP Model
OSI vs TCP/IP
TCP vs UDP
Three-Way Handshake
Four-Way Termination
What happens when you type a URL?
DNS
HTTP vs HTTPS
SSL vs TLS
IPv4 vs IPv6
Public vs Private IP
MAC Address vs IP Address
ARP
ICMP
Ping
Traceroute
DHCP
NAT
Router vs Switch vs Hub vs Bridge
Subnetting (CIDR basics)
Routing vs Forwarding
Static vs Dynamic Routing
RIP vs OSPF (basic idea)
Flow Control vs Congestion Control
Sliding Window
Go-Back-N vs Selective Repeat
FTP vs SFTP
SMTP vs POP3 vs IMAP
Ports (20/21, 22, 25, 53, 67/68, 80, 110, 143, 443)

One question worth mastering

Across Reddit discussions, Cisco experiences, and interviewer advice, the single question that stands out is:

"Explain everything that happens from the moment you type https://www.google.com into your browser until the page appears."

Answering this well naturally demonstrates your understanding of DNS, ARP, TCP, TLS, HTTP, routing, switching, IP addressing, and the OSI model—which is why many interviewers use it as a comprehensive networking question. (Reddit)

additionals

For SDE internships/fresher placements, you've already covered the four major Core CS subjects:

✅ Operating Systems
✅ DBMS
✅ Computer Networks
✅ OOP

These four account for the overwhelming majority of Core CS interview questions at companies like Amazon, Microsoft, Oracle, Adobe, Cisco, Goldman Sachs, Infosys, TCS, etc. (geeksforgeeks.org)

However, there are a few additional subjects that appear depending on the company and role.

1. Computer Organization & Architecture (COA) ⭐⭐⭐⭐

This is the next most common subject after the "big four."

It appears frequently in:

Qualcomm
NVIDIA
Intel
AMD
Cisco
Oracle
Samsung
Embedded/System Software roles

Typical questions actually reported:

Cache vs Main Memory
Cache Mapping
Direct Mapping
Associative Mapping
Virtual Memory vs Cache
Pipelining
Hazards
Branch Prediction
RISC vs CISC
Von Neumann vs Harvard
Registers
Interrupts
DMA
Endianness
Assembly basics
Addressing Modes

Qualcomm's OA explicitly included technical MCQs from OS, CN, DBMS, OOP, and C programming, with COA concepts commonly appearing in such hardware-oriented roles. (geeksforgeeks.org)

2. Compiler Design ⭐⭐⭐

Less common, but definitely asked.

Reported questions:

Lexical Analysis
Parser
Token
DFA vs NFA
Regular Expression
Symbol Table
Intermediate Code
Phases of Compiler
Syntax Tree

Reddit interview experiences mention candidates being asked Compiler Design and Theory of Computation questions, especially when interviewers wanted to probe CS fundamentals beyond the usual four subjects. (Reddit)

3. Theory of Computation (TOC) ⭐⭐

Mostly for:

Oracle
Research
Compiler
Higher-end product companies

Questions include:

DFA
NFA
Regular Expressions
PDA
CFG
Turing Machine
Chomsky Hierarchy

Usually only 1–2 questions.

4. Software Engineering ⭐⭐⭐

This has become more common recently.

Typical questions:

SDLC
Agile vs Waterfall
Scrum
Git workflow
Testing
Unit vs Integration Testing
Functional vs Non-functional Requirements
Design Patterns (basic)

Some recent placement preparation guides now explicitly include Software Engineering alongside OS, DBMS, CN, and OOP for freshers. (geeksforgeeks.org)

5. C/C++ Language Internals ⭐⭐⭐⭐

Many OAs include language-specific MCQs.

Common questions:

Pointer vs Reference
malloc() vs new
free() vs delete
const
volatile
Memory layout
Stack vs Heap
Virtual Functions
Vtable
Copy Constructor
Move Constructor (modern C++)
Shallow vs Deep Copy

Qualcomm, Oracle, and OFSS interview reports frequently mention C/C++ output and concept questions. (geeksforgeeks.org)

6. SQL (Beyond DBMS) ⭐⭐⭐⭐⭐

Although SQL is part of DBMS, companies often treat it as its own assessment.

Typical questions:

Write SQL
Optimize SQL
Window Functions
Recursive CTE
Index usage
Execution order

Many backend interviews spend more time on SQL than on DBMS theory.

7. Operating System + Linux Commands ⭐⭐

Sometimes asked:

grep
chmod
ps
kill
fork
top
lsof
netstat
Environment variables

Mostly in backend, DevOps, and infrastructure interviews.

8. Basic System Design ⭐⭐⭐

This has become increasingly common even for freshers.

Questions like:

Design Parking Lot
Design Library
Design URL Shortener
Design Chat App
Design Cache
Design TinyURL

Usually not distributed systems—more often Low-Level Design (LLD).

9. Aptitude & Logical Reasoning ⭐⭐⭐⭐

Still common in OAs for:

TCS
Infosys
Capgemini
Cognizant
Qualcomm
Accenture

Topics:

Probability
Time & Work
Number Series
Seating Arrangement
Coding-Decoding
Data Interpretation
Ratios
Speed & Distance

Qualcomm's OA, for example, explicitly included aptitude along with technical MCQs. (geeksforgeeks.org)

If you're targeting SDE internships at product companies

I would prioritize subjects in this order:

Priority	Subject	Importance
1	DSA	⭐⭐⭐⭐⭐
2	DBMS	⭐⭐⭐⭐⭐
3	Operating Systems	⭐⭐⭐⭐⭐
4	Computer Networks	⭐⭐⭐⭐
5	OOP	⭐⭐⭐⭐
6	SQL	⭐⭐⭐⭐
7	Computer Organization & Architecture	⭐⭐⭐
8	C/C++ language internals	⭐⭐⭐
9	Basic System Design	⭐⭐⭐
10	Aptitude	⭐⭐⭐
11	Software Engineering	⭐⭐
12	Compiler Design / TOC	⭐⭐

For your preparation

Given that you're targeting software engineering roles, I would recommend continuing in this order:

COA — the last major CS core subject that still appears regularly, especially in product companies.
SQL — focus on real interview query-writing questions.
C/C++ internals (or Java internals if interviewing in Java).
Low-Level Design (LLD) — increasingly common in fresher interviews.

Compiler Design and Theory of Computation are worth reviewing if you're applying to companies known for deeper CS interviews (e.g., Oracle, Qualcomm, NVIDIA) or compiler/systems roles, but they are much less common than the first six subjects. (geeksforgeeks.org)