1,230 questions from 240 interviews · updated from reports 2009-2026
About
Infosys is an Indian IT services and consulting company that builds and manages software, cloud, data, and business process systems for clients. In India, it often hires System Engineers, Software Engineers, and Digital Specialist Engineers for development, testing, support, and implementation work.
The roles that come up most are System Engineer, Software Engineer and Digital Specialist Engineer. This covers 240 candidate interviews reported from 2009 to 2026. Most sat it at entry level (220 of 235 that recorded a level), with 2 internship interviews alongside. Among the 185 that recorded either route, arrivals split between campus drives (50, 27%) and off-campus applications (135, 73%). Most questions fall under CS fundamentals and DSA.
Ans. SDLC is a structured process for planning, building, testing, deploying, and maintaining software. It gives teams a clear path from requirements to release, reducing risk and improving quality. Common stages include requirement analysis, design, implementation, testing, deployment, and maintenance, often repeated in agile or iterative models.
Ans. C++ is a compiled, statically typed language focused on performance and control, while Python is an interpreted, dynamically typed language focused on simplicity and fast development. The most important difference is that C++ gives manual control over memory and hardware-level details, whereas Python manages memory automatically but is usually slower.
Ans. ACID properties are the guarantees that make database transactions reliable: Atomicity, Consistency, Isolation and Durability. Atomicity means all or nothing, Consistency keeps valid rules, Isolation prevents concurrent transactions interfering, and Durability ensures committed changes survive crashes. They are essential for correctness in systems handling critical data.
Ans. Generate the Fibonacci series by starting with 0 and 1, then repeatedly adding the previous two numbers to get the next term until the required count is reached. Store the values in an array or list if they must be returned. The time complexity is O(n), with O(n) space, or O(1) if printed directly.
Ans. The SDLC phases are planning, requirements analysis, design, implementation, testing, deployment and maintenance. Planning defines scope and feasibility, requirements capture what users need, design describes the architecture, implementation builds it, testing verifies quality, deployment releases it, and maintenance fixes issues and improves the software over time.
Ans. SQL joins combine rows from related tables using a matching condition, usually a key. INNER JOIN returns only matching rows. LEFT JOIN returns all rows from the left table plus matches from the right. RIGHT JOIN is the reverse. FULL OUTER JOIN returns all rows from both sides. CROSS JOIN returns every combination of rows.
Ans. Common SDLC models include Waterfall, V-Model, Iterative, Incremental, Spiral, Prototype, RAD, Agile and Big Bang. The key difference is how they organise planning, design, development, testing and delivery. Waterfall is sequential, Agile is iterative and flexible, Spiral focuses on risk, and Prototype validates requirements early.
Ans. C is mainly a procedural systems programming language, while C++ extends C with object oriented and generic programming features. The key practical difference is that C++ provides classes, constructors, destructors, templates and a richer standard library, enabling abstractions such as RAII and containers while still supporting low level memory control.
Ans. Object-Oriented Programming models software as objects that combine data and behaviour. The main concepts are encapsulation, which hides internal state; abstraction, which exposes only needed details; inheritance, which reuses and extends existing classes; and polymorphism, which lets different objects respond to the same interface in their own way.
Ans. Use two pointers, one at the start of the string and one at the end, and compare characters while moving inward. If any pair differs, it is not a palindrome; if the pointers meet or cross, it is. This uses no extra data structure and runs in O(n) time with O(1) space.
Ans. A HashMap stores key value pairs in an internal array of buckets, using the key’s hashCode to choose a bucket index. If multiple keys land in the same bucket, it compares keys with equals and stores collisions in a linked list or, after enough collisions, a tree. Resizing happens when the load factor threshold is crossed.
Ans. Use backtracking to build permutations by choosing each unused character in turn, recursing until the current string has the original length, then print it. Keep a character array, a boolean used array, and a temporary result buffer. The time complexity is O(n × n!) and the recursion depth is O(n).
Ans. Use expand around centres: for each index, expand once for an odd-length palindrome and once between indices for an even-length palindrome, tracking the best start and length. The key detail is handling both centre types. This uses only a few variables, runs in O(n squared) time, and uses O(1) extra space.
Ans. Database normalization structures relational tables to reduce duplication and prevent update, insert, and delete anomalies. 1NF uses atomic values, 2NF removes partial dependency on a composite key, 3NF removes transitive dependency on non-key columns, and BCNF requires every determinant to be a candidate key. Higher forms handle multivalued and join dependencies.
Ans. A microprocessor is mainly a CPU that needs external memory and peripherals, while a microcontroller integrates the CPU, memory, timers and I/O on one chip. Microprocessors suit general-purpose, high-performance systems like PCs. Microcontrollers suit dedicated embedded tasks where cost, power use and compactness matter most.
Ans. Bubble sort repeatedly scans the array, compares adjacent elements, and swaps them if they are in the wrong order. After each full pass, the largest unsorted element moves to its final position. Stop after no swaps occur, or after n minus 1 passes. It sorts in place, with O(n²) time and O(1) space.
Ans. The OSI model has seven layers: physical, data link, network, transport, session, presentation and application. They describe how data moves from raw bits on a medium, through framing, routing and reliable delivery, up to user-facing protocols. The key idea is separation of concerns, so each layer provides services to the one above.
Ans. A primary key is a column, or set of columns, that uniquely identifies each row in a database table. The key detail is that its values must be unique and not null, so every record can be referenced reliably, often by foreign keys in related tables.
Ans. DDL commands define or change the database structure, while DML commands work with the data stored in those structures. Common DDL commands are CREATE, ALTER, DROP and TRUNCATE. Common DML commands are SELECT, INSERT, UPDATE and DELETE. The key difference is schema changes versus data manipulation.
Ans. I know bubble sort, selection sort, insertion sort, merge sort, quicksort, heap sort, counting sort, radix sort and bucket sort. The main detail is their trade off: comparison sorts are usually O(n log n) at best for general data, while non-comparison sorts can be linear when keys fit suitable constraints.
Ans. C is a compiled, statically typed, low-level language, while Python is an interpreted, dynamically typed, high-level language. The main practical difference is control versus productivity: C gives direct memory control and fast execution, while Python is easier to write and read but usually slower and relies on automatic memory management.
Ans. Selection sort repeatedly finds the smallest element in the unsorted part of the array and swaps it with the first unsorted position. After each pass, one more element is in its final place. It runs in O(n²) time in best, average, and worst cases, with O(1) extra space.
Ans. A DBMS stores and manages data, while an RDBMS is a type of DBMS that stores data in related tables. The key difference is that an RDBMS enforces relationships using keys, such as primary and foreign keys, and usually supports SQL, constraints, normalisation, and stronger data integrity rules.
Ans. Swap them using arithmetic: set the first number to the sum of both, set the second to the new first minus the second, then set the first to the new first minus the new second. This uses constant space and constant time. The key caveat is integer overflow, so a temporary variable is usually safer.
Ans. A stack removes the most recently added item first, while a queue removes the earliest added item first. This is usually called LIFO for stack and FIFO for queue. Stacks are used for function calls, undo, or parsing. Queues are used for scheduling, buffering, and breadth first search.
Ans. The UPDATE statement syntax is: update a table, set one or more column values, and optionally restrict rows with a WHERE condition. The key detail is that omitting WHERE updates every row in the table, so it should be used carefully, often after checking the matching rows with a SELECT.
Ans. Abstraction in Object-Oriented Programming is the idea of exposing only the essential features of an object while hiding unnecessary implementation details. The key detail is that it lets users work with what an object does, not how it does it, often through interfaces, abstract classes, and public methods.
Ans. Encapsulation is the practice of keeping an object’s data and the methods that operate on it together, while hiding internal details from outside code. The key point is controlled access: fields are usually private, and other code interacts through public methods, which helps protect invariants and reduce unintended dependencies.
Ans. A process is an independent running program with its own memory space, while a thread is a smaller unit of execution within a process that shares that process’s memory. Processes are more isolated and cost more to create or switch between. Threads are lighter, but shared memory makes synchronisation and race conditions important.
Ans. The four pillars of object-oriented programming are encapsulation, abstraction, inheritance, and polymorphism. Encapsulation hides internal state behind methods. Abstraction exposes only essential behaviour. Inheritance lets classes reuse and extend other classes. Polymorphism lets different objects be treated through the same interface while providing their own behaviour.
Ans. An array stores elements in contiguous memory, while a linked list stores elements in separate nodes connected by pointers. Arrays give fast index access in O(1) but insertions and deletions often cost O(n). Linked lists need O(n) to access an index, but can insert or delete in O(1) when the node is known.
Ans. SQL databases store structured data in tables with fixed schemas and use SQL for relational queries. NoSQL databases use more flexible models such as documents, key value pairs, columns, or graphs. The key difference is that SQL favours strong consistency and complex joins, while NoSQL often favours flexibility, scale, and high availability.
Ans. Use a dummy head and a tail pointer, then repeatedly attach the smaller current node from the two sorted linked lists. Advance the chosen list and the tail each time. When one list ends, attach the remaining nodes from the other list. This runs in O(n + m) time and O(1) extra space.
Ans. 2-tier architecture has a client layer talking directly to a database or server, while 3-tier architecture separates the system into client, application or business logic, and database layers. The key difference is that 3-tier centralises business logic in a middle tier, improving maintainability, security, scalability, and reuse compared with direct client to database access.
Ans. DROP removes the table itself, including its definition and data; DELETE removes selected rows; TRUNCATE removes all rows but keeps the table structure. DELETE can use a WHERE clause and is usually fully logged. TRUNCATE is faster, often resets identity values, and cannot target specific rows. Behaviour can vary by database.
Ans. An abstract class is a base class that can share state and implemented behaviour, while an interface defines a contract that classes agree to implement. The key detail is inheritance: a class usually extends one abstract class, but can implement multiple interfaces, making interfaces better for capabilities across unrelated classes.
Ans. Identify the topic first, such as percentages, ratios, averages, time and work, profit and loss, or speed. Write down the given values, choose the relevant formula, and simplify step by step. Use estimation to check whether the answer is reasonable, and avoid lengthy calculations by cancelling, approximating, or using shortcuts where appropriate.
Ans. Method overloading means defining multiple methods with the same name but different parameter lists in the same class, while method overriding means a subclass provides its own implementation of a method already defined in its parent class. Overloading is resolved at compile time, whereas overriding is resolved at runtime using dynamic dispatch.
Ans. The main types of inheritance are single, multiple, multilevel, hierarchical and hybrid inheritance. Single means one parent class, multiple means several parents, multilevel forms a chain, hierarchical means many child classes share one parent, and hybrid combines patterns. Some languages, such as Java, restrict multiple class inheritance to avoid ambiguity.
Ans. Function overloading means defining multiple functions with the same name but different parameter lists, while function overriding means a subclass provides its own implementation of a method already defined in its superclass. Overloading is resolved at compile time in many languages; overriding is resolved at run time using dynamic dispatch.
Ans. Use the Sieve of Eratosthenes up to a safe upper bound, then count primes until the nth is reached. Store primality in a boolean array and mark multiples of each prime as composite. For n greater than 6, a common bound is n log n plus n log log n. Time is O(limit log log limit).
Ans. A red-black tree is a self-balancing binary search tree where each node has a colour, red or black, used to keep the tree approximately balanced. Its rules, such as no two red nodes in a row and equal black height on all root-to-leaf paths, ensure search, insert, and delete take O(log n) time.
Ans. We use heap sort when we need guaranteed O(n log n) sorting time and want to sort in place with little extra memory. It is useful when worst case performance matters more than stability. The main trade-off is that heap sort is not stable and is often slower in practice than quicksort due to poorer cache locality.
Ans. volatile is a qualifier telling the compiler that an object’s value may change in ways it cannot see, so each access must actually be performed. It is mainly used for memory-mapped hardware registers, signal handlers, or similar low-level cases. It does not make operations atomic or provide thread synchronisation in C++.
Ans. N-tier architecture is a software design that splits an application into separate logical layers, or tiers, such as presentation, business logic, and data access. Each tier has a clear responsibility and communicates with adjacent tiers. The key benefit is separation of concerns, making the system easier to maintain, scale, test, and change.
Ans. File handling in C++ is done using stream classes from the fstream library: ifstream for reading, ofstream for writing, and fstream for both. A file is opened with a mode such as input, output, append, or binary, then data is read or written using stream operators or functions. Always check the stream state for errors.
Ans. Codd’s rules are a set of 13 rules, numbered 0 to 12, that define what a true relational DBMS should support. They cover storing data as tables, using relational operations, handling nulls, enforcing integrity, ensuring logical and physical data independence, and providing access through a relational language such as SQL.
Ans. Dijkstra’s algorithm finds the shortest path from a source node to all other nodes in a weighted graph with non-negative edge weights. It keeps tentative distances, repeatedly picks the unvisited node with the smallest distance using a priority queue, and relaxes its neighbours. With an adjacency list, it runs in O((V + E) log V).
Ans. Garbage collection in Java is automatic memory management that finds objects no longer reachable by the program and reclaims their heap memory. The key point is reachability from roots such as stack variables, static fields and active threads. It reduces manual memory errors, but collection timing is not deterministic and may briefly pause execution.
Ans. Shortest path algorithms find the minimum-cost route between vertices in a graph. Use BFS for unweighted graphs, Dijkstra’s algorithm with a priority queue for non-negative edge weights, Bellman-Ford when negative weights may exist, and Floyd-Warshall for all-pairs shortest paths. The key detail is matching the algorithm to edge weights and query type.
Ans. Use work rate: if a person finishes a job in n days, their rate is 1/n of the job per day. Add rates when people work together, subtract for leaks or inefficiency, then use time = total work ÷ combined rate. Keep units consistent and use LCM if fractions are awkward.
Ans. Build a service with create and redirect APIs, storing short code to long URL mappings in a durable key-value store. Generate codes using a unique ID encoded in Base62, or random codes with collision checks. The critical detail is read scalability: cache popular mappings and make redirects fast, while writes can be slower.
Ans. Build a service with create and redirect APIs, storing short code to long URL mappings in a durable key value store. The most important detail is generating unique, non-guessable codes: use a distributed ID generator or random 62-character tokens with collision checks. Cache hot redirects, use 301 or 302 intentionally, and track basic analytics asynchronously.
Ans. Identify the shape or triangle first, then write the relevant formula before substituting values. For mensuration, track units and split complex figures into standard parts. For trigonometry, draw a diagram, mark angles and sides, choose identities or sine, cosine and tangent rules, then simplify carefully and check whether the answer is reasonable.
Ans. Pick a situation with real time pressure, competing demands, and a clear result. Emphasise how you stayed calm, clarified deadlines, assessed impact, communicated trade-offs, and focused on the highest-value work first. Interviewers listen for structure, judgement, ownership, and evidence that pressure improves your focus rather than causing confusion.
Ans. Use a structured method: clarify the rules, list known facts, identify constraints, test small cases, and eliminate impossibilities. If numbers are involved, look for invariants, parity, or patterns. Explain each step aloud so the interviewer sees your reasoning, not just the final answer. Without a specific puzzle, there is no single result.
Ans. Expose books as the main resource: GET /books with pagination and filters, POST /books to create, GET /books/{id}, PUT or PATCH /books/{id}, and DELETE /books/{id}. Use JSON with fields such as id, title, author, isbn and publishedYear. Return correct HTTP status codes, validate input, and keep errors consistent.
Ans. The next number is 20. Split the series into two alternating sequences. The 1st, 3rd and 5th terms are 80, 70, 60, decreasing by 10. The 2nd, 4th and 6th terms are 10, 15, so they increase by 5. Therefore the missing term is 20.
Ans. Choose a real conflict with moderate stakes, not personal drama. Emphasise listening to each side, clarifying facts and goals, separating people from the problem, agreeing actions, and following up. Interviewers listen for calm judgement, fairness, ownership, communication, and evidence that you protect relationships while still moving the project forward.
Ans. A strong answer should show informed, balanced judgement without sounding partisan. Refer to the farmers’ bill dispute as a policy issue affecting livelihoods, markets and trust in consultation. Emphasise empathy for farmers, respect for lawful protest, and the need for transparent dialogue. Interviewers listen for maturity, fairness and evidence-based thinking.
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Candidate interviews most often cover CS fundamentals (61%) and DSA (28%).
Candidate interviews show an average of 2.5 rounds per experience, with a typical sequence of Online test → Technical. Individual interview paths can vary.
Among questions with a recorded difficulty, the mix is easy 60%, medium 35%, hard 5%.
