473 questions from 77 interviews · updated from reports 2015-2025
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IBM is a technology company that provides software, cloud services, consulting, and IT infrastructure services to businesses and governments. In India, it is known for hiring Associate System Engineers, Software Engineers, Software Developers, and other entry-level technical roles.
The roles that come up most are Associate System Engineer, Software Engineer and Software Developer. This covers 77 candidate interviews reported from 2015 to 2025. Most sat it at entry level (64 of 76 that recorded a level), with 10 internship interviews alongside. Among the 62 that recorded either route, arrivals split between campus drives (49, 79%) and off-campus applications (13, 21%). Most questions fall under CS fundamentals and DSA.
Ans. Read the sentence slowly and check one issue at a time: subject verb agreement, tense, articles, prepositions, pronouns, modifiers, parallel structure, and word order. Look for unnecessary words and common idiom errors. If no error is visible, ensure the sentence is grammatically complete and conveys a clear meaning.
Ans. Identify the familiar root word first, then check common trouble points such as double letters, silent letters, vowel order, and suffix changes. Say each option slowly, but do not rely only on sound. Eliminate spellings that break standard patterns. If unsure, choose the version you have seen in formal writing.
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. Use dynamic programming where each cell stores the number of ways to reach it, treating obstacle cells as zero paths. Initialise the start as 1 if it is not blocked, then for each open cell add paths from the top and left. A one-dimensional array over columns is enough. Time is O(mn), space is O(n).
Ans. Use dynamic programming with a hash set of the words. Let dp[i] mean the prefix s[0..i) can be formed. Set dp[0] true, then for each i check earlier j values where dp[j] is true and s[j..i) is in the set. The time complexity is O(n²) substring checks, with O(n) space.
Ans. Binary search repeatedly halves a sorted array or list to find a target value. Keep two indexes, low and high, check the middle element, and move to the left half if the target is smaller or the right half if it is larger. It runs in O(log n) time and O(1) space iteratively.
Ans. Virtualization is the creation of a software-based version of a physical resource, such as a server, operating system, storage device, or network. The key idea is abstraction: one physical machine can run multiple isolated virtual machines. It is used in cloud computing, server consolidation, testing environments, disaster recovery, and running legacy applications.
Ans. Read the word carefully and decide its exact meaning in the sentence, if context is given. For synonyms, choose the option closest in meaning, not just vaguely related. For antonyms, choose the clearest opposite. Eliminate options with wrong tone, part of speech, or intensity. Check common prefixes and roots when unsure.
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. AWS, Azure and Google Cloud are the main public cloud platforms, offering compute, storage, databases, networking, security and managed services. AWS is broad and mature, Azure integrates strongly with Microsoft ecosystems, and Google Cloud is strong in data and Kubernetes. Common frameworks include serverless, containers and infrastructure as code.
Ans. Use a monotonic decreasing stack to store previous prices with their accumulated spans. For each price, start span as 1, pop while the stack top price is less than or equal to current price, adding its span. Push the current price and total span, then output it. Each price is pushed and popped once, so time is O(n).
Ans. A v-table, or virtual table, is a compiler-generated table used to implement dynamic dispatch for virtual functions in C++. Each polymorphic class typically has one table of function pointers, and each object stores a hidden pointer to it. At runtime, calls to virtual functions are resolved through this table.
Ans. A Max Heap is a complete binary tree where every parent node is greater than or equal to its children, so the maximum value is always at the root. It is usually stored in an array. Insertion and deletion restore order by bubbling values up or down, taking O(log n) time.
Ans. React works by turning components into a tree of elements, comparing new output with the previous tree, and applying only necessary changes to the real DOM. The key detail is Fiber, React’s internal tree and scheduler, which breaks rendering into units of work so updates can be prioritised, paused, resumed, and committed efficiently.
Ans. STL in C++ is built around containers, iterators and algorithms. Containers such as vector, list, map and set store data. Iterators provide a common way to traverse them. Algorithms such as sort, find and count work through iterators, so the same algorithm can operate on many container types.
Ans. Use dynamic programming: at each house, choose the maximum of robbing it plus the best up to two houses before, or skipping it and keeping the best up to the previous house. Store only two variables, prev2 and prev1, since older values are unnecessary. Time complexity is O(n), space complexity is O(1).
Ans. Virtual memory is an abstraction that gives each process its own large, private address space, independent of physical RAM. Paging implements this by splitting virtual memory and physical memory into fixed-size pages and frames. A page table maps virtual pages to frames, and missing pages can be loaded from disk on demand.
Ans. Use dynamic programming where dp[i] is the maximum sum of an increasing subsequence ending at index i. Initialise dp[i] to arr[i], then for each j before i, if arr[j] < arr[i], update dp[i] with dp[j] + arr[i]. The answer is the maximum value in dp. Time complexity is O(n²), space is O(n).
Ans. Recursion works by a function calling itself, with each call getting its own stack frame containing parameters, local variables and return address. Calls keep stacking until a base case stops further calls. Then the stack unwinds, each call returns to its caller, and results are combined if needed. Excessive depth can cause stack overflow.
Ans. At runtime, memory is mainly allocated on the stack for function calls and local values, and on the heap for objects whose lifetime is not tied to one function. Stack allocation is automatic and fast. Heap allocation is managed by an allocator, and memory is freed manually or by garbage collection, depending on the language.
Ans. The virtual keyword in C++ marks a member function for runtime polymorphism, so the version called is chosen based on the actual object type, not the pointer or reference type. It is used in base classes for functions meant to be overridden. Base classes should usually have a virtual destructor if deleted polymorphically.
Ans. Use Floyd’s slow and fast pointer method. Start both at the head, move slow one step and fast two steps each time. If they ever meet, there is a cycle. If fast reaches null, there is no cycle. This uses no extra data structure, runs in O(n) time and O(1) space.
Ans. Virtual memory is an operating system technique that gives each process the illusion of a large, private, continuous address space, mapped to physical RAM and sometimes disk. Its main benefits are isolation between processes, simpler memory management for programs, efficient sharing of memory, and the ability to run programs larger than available RAM.
Ans. Choose a real conflict where the stakes were meaningful but professional, not personal drama. Emphasise listening first, separating facts from assumptions, agreeing on shared goals, and finding a practical resolution. Interviewers listen for emotional control, ownership, respect for others, clear communication, and evidence that the relationship and work both improved.
Ans. A DBMS is software that stores, organises and retrieves data while enforcing rules for correctness and access. The key fundamentals are schemas, tables, keys, relationships, SQL, indexing, normalisation, transactions and concurrency control. The most important detail is ACID transactions, which keep data consistent even with failures or simultaneous users.
Ans. A shallow copy copies the object’s member values as they are, so pointer members still point to the same memory. A deep copy creates new owned resources and copies the pointed-to data too. The key issue is ownership: shallow copies of owning raw pointers can cause shared mutation, dangling pointers, or double deletion.
Ans. A memory leak is memory that is allocated but never released, so the program gradually uses more memory. Memory corruption is when a program writes to or reads from memory it should not, damaging data or control information. The key difference is that leaks waste memory, while corruption can cause crashes, wrong results, or security bugs.
Ans. AWS and GCP are both major cloud platforms, but AWS has the largest service catalogue and market share, while GCP is strongest in data analytics, machine learning, Kubernetes and global networking. AWS is often chosen for maturity and breadth. GCP is often chosen for simpler pricing, BigQuery, and cloud-native engineering.
Ans. RAG is a technique where a generative AI model retrieves relevant external information before producing an answer. Instead of relying only on what the model learned during training, it searches sources such as documents, databases, or vector indexes, then uses that context to generate a more accurate and up-to-date response.
Ans. Java 8 introduced lambda expressions, functional interfaces, the Stream API, default and static methods in interfaces, Optional, the new Date and Time API, method references, and CompletableFuture improvements. The most important change was functional-style programming, where lambdas and streams made collection processing more concise, expressive, and easier to parallelise.
Ans. A browser renders a web page by fetching resources, parsing HTML into the DOM, parsing CSS into the CSSOM, combining them into a render tree, then doing layout, painting and compositing. The key detail is that JavaScript and CSS can block or change this pipeline, causing reflow or repaint when the page changes.
Ans. In AWS, a public key is stored or shared to identify and encrypt for you, while the private key is kept secret and used to prove identity or decrypt. For EC2 key pairs, AWS keeps the public key on the instance, and you use the private key to SSH in securely.
Ans. Scan the prefix expression from right to left using a stack. When you see an operand, push it. When you see an operator, pop the top two expressions, combine them as first second operator, and push the result back. At the end, the stack top is the postfix expression. Time and space complexity are O(n).
Ans. SSH is a secure protocol for remote login and command execution, while socket programming is the way applications create network connections. SSH usually runs over TCP port 22 and uses encryption plus password or key authentication. Sockets expose endpoints where programs bind, listen, connect, send, and receive data using TCP or UDP.
Ans. Pick a real example where you faced reasonable pushback, not stubborn opposition. Emphasise listening first, testing assumptions, using data, adapting the idea, and giving credit to others. Interviewers listen for humility, collaboration, resilience, and whether you can influence without authority while still keeping the team goal ahead of your ego.
Ans. C++20 is a much larger update than C++14, adding major language features such as concepts, ranges, modules, coroutines, the three-way comparison operator, and broader constexpr support. C++14 mainly refined C++11 with generic lambdas, return type deduction, variable templates, and make_unique. The biggest practical difference is clearer generic programming with concepts.
Ans. A critical section is a part of a program where shared resources, such as variables, files or data structures, are accessed and must not be used by multiple threads at the same time. It is handled using synchronisation mechanisms such as locks, mutexes, semaphores or monitors to ensure mutual exclusion and prevent race conditions.
Ans. Flatten it with a depth-first traversal, placing each child list immediately after its parent before continuing with the saved next node. Use recursion that returns the tail, or an explicit stack to remember next pointers. Set each child pointer to null after splicing. This visits each node once, so time is O(n) and space is O(depth).
Ans. SQL injection is an attack where untrusted input is treated as part of an SQL command, allowing an attacker to read, change, or delete data. Prevent it by using parameterised queries or prepared statements, so values are bound separately from SQL code. Also validate input and use least-privilege database accounts.
Ans. Threads are independent paths of execution within the same process, sharing its memory and resources. Compared with processes, they are usually faster to create, cheaper to switch between, and simpler for sharing data. The key trade-off is that shared memory requires careful synchronisation to avoid race conditions and deadlocks.
Ans. If every pair of points can be joined directly and direction does not matter, the number is N(N-1)/2. This is choose 2 because each path is defined by two endpoints, and A to B is the same as B to A. If direction matters, use N(N-1).
Ans. Interrupts are signals that make the CPU pause its current work and run a special handler for an event. The CPU saves its current state, jumps to the interrupt service routine, handles the event, then restores the saved state and continues. They let hardware or software get immediate attention without constant polling.
Ans. Iterators in C++ are objects that act like pointers to elements in a container, letting you traverse and access values. A range is a sequence of elements represented by a beginning and an end, often begin and end iterators. Most standard algorithms work on ranges, usually using half-open intervals: begin included, end excluded.
Ans. Software design patterns are reusable solutions to common design problems, such as object creation, behaviour coordination, or structuring relationships between classes. The most important point is to use them to improve clarity, flexibility, and maintainability, not to force them into simple code where they add unnecessary complexity.
Ans. Paging divides memory into fixed-size pages and frames, while segmentation divides a program into variable-size logical units such as code, stack and data. Paging avoids external fragmentation but can have internal fragmentation. Segmentation matches the programmer’s view and supports protection per segment, but suffers from external fragmentation and may need compaction.
Ans. A Turing machine is a theoretical model of computation with an infinite tape, a read/write head, states, and rules; a finite automaton is a simpler model with a finite number of states and input transitions. The key difference is memory: Turing machines have unbounded memory, while finite automata have only state memory.
Ans. C++ is a compiled, statically typed language that supports procedural, object-oriented and generic programming. The key concept is resource management: prefer RAII, where objects acquire resources in constructors and release them in destructors, using standard library containers and smart pointers instead of manual memory management where possible.
Ans. Operating systems manage hardware resources and provide services for programs. The core ideas are processes and threads, CPU scheduling, memory management, file systems, system calls, synchronisation, deadlocks and I/O management. The most important detail is that the OS abstracts hardware while enforcing isolation, fairness and efficient resource sharing among running programs.
Ans. Use the permission bits: read is 4, write is 2, execute is 1, and add them for user, group and others. For example, rwxr-xr-- becomes 754: user 4+2+1, group 4+1, others 4. Special bits may add a leading digit.
Ans. Cache memory is commonly implemented using a hash table for fast lookup. In many software caches, such as an LRU cache, a hash map is combined with a doubly linked list so items can be found, inserted, removed, and reordered in constant time on average.
Ans. Expand around every possible centre and keep the longest palindrome seen. For each index, check both odd length and even length centres, moving left and right while characters match. This uses constant extra space and runs in O(n²) time, which is usually acceptable unless Manacher’s O(n) algorithm is specifically required.
Ans. Use a one-dimensional DP array where dp[x] stores the minimum number of coins needed to make amount x. Initialise dp[0] to 0 and all other entries to infinity, then for each amount try every coin and update dp[x]. The answer is dp[amount], or -1 if unreachable. Time is O(amount × coins), space is O(amount).
Ans. Use a running prefix sum and a hash map of prefix sum frequencies. For each element, update the prefix sum, then add the number of times prefix sum minus K has been seen, because those starts form subarrays ending here. Store the current prefix sum. Initialise sum 0 with frequency 1. Time is O(n), space is O(n).
Ans. Pick a real situation where something changed suddenly, such as a deadline, mistake, conflict, or missing resource. Emphasise how you stayed calm, assessed priorities, communicated early, and took practical action. Interviewers listen for ownership, judgement, resilience, and learning, not a perfect outcome or blame placed on others.
Ans. With only one non-uniform rope, you cannot reliably measure 45 minutes. Lighting one end gives 60 minutes, and lighting both ends gives 30 minutes, but there is no known point for 45. The standard 45-minute solution needs two such ropes: use one to mark 30 minutes, then the other to mark 15 more.
Ans. Design around product discovery, accurate inventory, pricing, promotions, checkout speed, delivery or pickup slots, payments, substitutions, and customer support. The most important detail is real-time stock and fulfilment integration by store, because grocery customers need reliable availability, fresh items, and delivery promises that match local operations.
Ans. The answer depends on the objects shown, so I would recreate the scene systematically. I would first recall the overall layout, then group items by position, colour, shape, or category. I would mentally scan left to right and check for anything unusual, because distinctive details are usually easiest to recover accurately.
Ans. Microservices commonly communicate synchronously through HTTP REST or gRPC, and asynchronously through messaging such as Kafka or RabbitMQ. An API Gateway is the single entry point for clients, handling routing, authentication, rate limits and aggregation. RestTemplate is Spring’s older synchronous HTTP client for service-to-service REST calls, usually combined with timeouts, retries and service discovery.
Ans. I would create a short code for each long URL, store the mapping in a database, and redirect requests by looking up that code. The key detail is generating unique codes reliably, often with an atomic counter or distributed ID generator encoded in Base62. Add caching for popular links, expiry rules, and analytics if needed.
Ans. Minimum is 7 races. Race five groups of five. Race the five winners. The winner of that race is fastest. Only horses that could still be second or third are: second and third from the fastest winner’s group, first and second from the second fastest winner’s group, and first from the third fastest winner’s group. Race those five. Top two complete the top three.
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Candidate interviews most often cover CS fundamentals (44%) and DSA (30%).
Candidate interviews show an average of 3.9 rounds per experience, with a typical sequence of Online test → Online test → Group discussion → Technical. Individual interview paths can vary.
Among questions with a recorded difficulty, the mix is easy 58%, medium 40%, hard 2%.
