106 questions from 17 interviews · updated from reports 2017-2025
About
Quantiphi is a technology services company that works on artificial intelligence, data, cloud, and software engineering projects for business clients. In India, it is known for hiring software engineers, framework engineers, analysts, data engineers, and cloud or machine learning engineers.
The roles that come up most are Framework Engineer, Software Engineer and Analyst. This covers 17 candidate interviews reported from 2017 to 2025. Most sat it at entry level (15 of 15 that recorded a level). Among the 10 that recorded either route, arrivals split between campus drives (10, 100%). Most questions fall under CS fundamentals and DSA.
Ans. Use joins by selecting columns from related tables and matching their keys in the join condition. For example, join customers to orders on customer id to return each order with its customer details. Use inner join for matching rows, left join to keep all rows from the left table, and filter with where.
Ans. Use Subarray Sum Equals K and Merge Intervals as good medium DSA examples. For Subarray Sum, use prefix sums with a hash map to count earlier sums, in O(n) time. For Merge Intervals, sort by start time, scan once, and merge overlaps, in O(n log n) time.
Ans. Socket.IO is a JavaScript library for real-time, bidirectional communication between a client and a server. It is commonly used in chat apps, live notifications, dashboards, multiplayer games and collaboration tools. The key detail is that it uses WebSockets when possible, with fallback transport support for reliability.
Ans. The output depends on constructor calls, method overriding, inheritance, access modifiers and runtime polymorphism in the given code. Trace object creation first, then static initialisation, constructor chaining, overloaded versus overridden methods, and finally the actual reference and object types used in each call. Without the code, no exact output can be predicted.
Ans. A strong answer names a product tied to a real user problem you understand. Pick something specific, not a vague platform. Emphasise who it helps, the pain it solves, why now, and how you would measure success. Interviewers listen for customer focus, prioritisation, commercial sense, and enthusiasm grounded in evidence.
Ans. I would practise Longest Substring Without Repeating Characters, Number of Islands, and Top K Frequent Elements. They cover sliding window with a hash set in O(n), graph traversal using DFS or BFS in O(mn), and heap or bucket counting with a hash map, usually O(n log k) or O(n).
Ans. Use Node.js with Express to create an HTTP server, define routes such as GET for reading data and POST for creating data, and start listening on a port. Store sample data in an in-memory array or object. Route lookup is handled by Express, and basic operations are typically constant time except searches, which are linear.
Ans. Break revenue into drivers: number of customers, average order value, visit frequency, and table turnover. Identify the biggest constraint using data, then target actions such as better pricing, upselling, menu engineering, delivery, promotions, loyalty schemes, faster service, or longer opening hours. Prioritise ideas by expected impact, cost, risk, and time to implement.
Ans. Use an array of buckets, compute an index with a custom hash function, and store colliding keys in a small list at that bucket. For strings, multiply the running hash by a prime and add each character value, then take modulo capacity. Insert, search, and delete are average O(1), worst-case O(n).
Ans. A Java String is immutable, meaning once created its character sequence cannot be changed. Operations like concat or replace create new String objects instead. This enables safe sharing, String pool interning, cached hash codes, and thread safety. For many modifications, use StringBuilder or StringBuffer to avoid creating many temporary objects.
Ans. Use an optimised Sieve of Eratosthenes up to an estimated upper bound for the Nth prime, then return the Nth number still marked prime. Store primality in a boolean array and cross out multiples from p squared. A good bound is n(log n + log log n). Time is O(m log log m), space is O(m).
Ans. Use explicit joins with clear join predicates, then apply DML carefully with filters and transactions. For example, an inner join returns matching rows, a left join keeps unmatched rows from the left table, and update or delete statements should usually be tested as selects first. The key detail is avoiding accidental many-to-many matches.
Ans. Use a window function such as DENSE_RANK over salaries ordered descending, then select the row where the rank equals N. DENSE_RANK handles duplicate salaries correctly by treating equal salaries as the same rank. The database will usually sort the salary values, so the main cost is sorting, typically O(n log n).
Ans. Thread synchronization is coordinating multiple threads so they access shared data safely and in the correct order. It is usually done with locks, mutexes, semaphores or monitors. Deadlocks can be overcome by preventing circular wait, acquiring locks in a fixed order, using timeouts, releasing resources on failure, or detecting and breaking deadlocked cycles.
Ans. A DBMS stores, organises and controls access to data, while SQL is used to query and modify that data. Key concepts include tables, keys, relationships, normalisation, indexes, transactions and ACID properties. For queries, identify the required rows, joins, filters, grouping and ordering, then consider correctness and performance.
Ans. Circular covers cannot fall through their own openings, because every width across a circle is the same diameter. A square or rectangular cover can be turned diagonally and may drop through the hole. Circles are also easy to roll, do not need alignment when replaced, and spread loads evenly.
Ans. A DBMS stores, organises, queries, and protects data while managing concurrent access. Core ideas are tables, rows, columns, schemas, primary and foreign keys, relationships, SQL queries, indexes, constraints, normalisation, and transactions. The most important theory detail is ACID: transactions should be atomic, consistent, isolated, and durable.
Ans. Add a click event listener to the button and, inside the handler, update the table element’s background colour, preferably by toggling a CSS class. Store references to the button and table DOM elements. The operation is constant time, as it only changes one element’s style or class.
Ans. Identify what is being asked, list the given facts, and convert words into equations, ratios, tables, or diagrams. Use estimation first to spot impossible options, then calculate carefully. For logic questions, track conditions step by step and eliminate contradictions. Check units, assumptions, and whether the final answer fits the question.
Ans. MVC separates an application into Model, View and Controller, where the model holds data and business state, the view renders output, and the controller handles requests and coordinates flow. In Spring Boot, controllers are classes annotated with Controller or RestController, services contain business logic, repositories access data, and views are templates or JSON responses.
Ans. Convert n to binary and replace each set bit at position i with 5 to the power i, using positions starting at 1. For example, 3 is binary 11, so the answer is 5¹ + 5² = 30. Iterate through bits of n, accumulate powers of 5. Time complexity is O(log n).
Ans. An abstract class is a partial base class, while an interface is mainly a contract a class agrees to implement. An abstract class can hold instance state, constructors, and concrete methods, but a class can extend only one. A class can implement multiple interfaces, which is useful for defining shared capabilities.
Ans. Java Collections Framework is a set of interfaces and classes for storing, accessing and manipulating groups of objects. List stores ordered elements and allows duplicates, Set stores unique elements with no guaranteed order unless specified, and Map stores key value pairs with unique keys. The key detail is choosing by access pattern and uniqueness needs.
Ans. Use a hash map to store counts of numbers seen so far, then for each value x, look up k minus x and output pairs for any previous occurrences. This handles an unsorted array in one pass, including duplicates if counts are used. Time is O(n plus output size), space is O(n).
Ans. Use a 2D Fenwick tree or 2D segment tree to support efficient matrix queries with updates. Store aggregate values for subrectangles, update one cell by propagating the difference through the structure, and answer rectangular searches or sums by combining prefix results. Point update and range query take O(log n log m) time.
Ans. The output depends on whether the function only reads a global name or assigns to that name. Reading uses the global value if no local exists. Any assignment inside a function makes that name local unless declared global, so reading it before assignment raises UnboundLocalError. global makes assignments update the module-level variable.
Ans. Polymorphism means one interface can represent different underlying behaviours. Compile-time polymorphism is method or operator overloading, where the compiler chooses the correct function from the argument types. Run-time polymorphism is method overriding, where a base class reference calls a derived class method through dynamic dispatch. For example, Shape.draw() can call Circle.draw() or Square.draw().
Ans. React hooks let function components hold state, run side effects, and keep values across renders. useState stores reactive UI data like form input or toggles. useEffect runs after render for tasks such as fetching data, subscriptions, or syncing with browser APIs. useRef stores mutable values or DOM references without causing re-renders.
Ans. Validate each barcode against the required format and checksum, and return the one that fails. In Python, iterate through the barcode list, use a set or dictionary to track valid references if needed, and apply the checksum rule character by character. This takes O(n·m) time, where n is barcodes and m is barcode length.
Ans. Synchronous console.log calls run first, in the order they appear, and setTimeout callbacks run later, after the call stack is empty. Even a setTimeout with 0 milliseconds does not run immediately. The key detail is the event loop: timers are queued as macrotasks, after synchronous code and pending microtasks.
Ans. Rank players using a weighted score based on role-specific performance measures, such as batting average, strike rate, bowling average, economy, fielding, and recent form. Also consider fitness, consistency, match conditions, team balance, opposition, and pressure handling. Select the player who best fits the required role and improves the overall team combination.
Ans. In multilevel inheritance, constructors run from the topmost base class down to the most derived class, while destructors run in the reverse order. For example, if C inherits from B and B inherits from A, creating C calls A, then B, then C. Destroying it calls C, then B, then A.
Ans. Use Dijkstra’s algorithm from the source if all edge weights are non-negative. Store the graph as an adjacency list and use a min-priority queue to repeatedly process the node with the smallest known distance, relaxing outgoing edges. The time complexity is O((V + E) log V). Use Bellman-Ford if negative weights exist.
Ans. Choose a real example where hotels, transport, attractions and local partners coordinated to improve a guest journey. Emphasise shared customer data, joined-up booking, clear communication, service standards and quick problem solving. Interviewers listen for collaboration, commercial awareness, customer focus, practical execution and evidence that the approach improved satisfaction or repeat business.
Ans. Multiple inheritance means a class inherits behaviour or state from more than one parent class. Java does not support multiple inheritance of classes, mainly to avoid ambiguity such as the diamond problem. It supports multiple inheritance of type through interfaces. Similar designs are implemented using interfaces, default methods, composition, and delegation.
Ans. Relational databases store structured data in tables with schemas and SQL, while non-relational databases use flexible models like documents, key value or graphs. Vertical scaling adds resources to one machine; horizontal scaling adds more machines. Sharding splits data across machines, often by customer or region, useful for high traffic, large datasets and multi-tenant systems.
Ans. Use dynamic programming: for each element, decide whether to take it plus the best sum up to two positions before, or skip it and keep the best sum up to the previous position. Keep only two variables, previous and previous previous, since older values are not needed. Time complexity is O(n), space is O(1).
Ans. Inheritance lets a class reuse and extend another class, for example Car inheriting from Vehicle and adding boot size. Public members are accessible everywhere, protected members in the class and subclasses, private members only inside the class. With public inheritance access is preserved; protected inheritance makes inherited public/protected protected; private inheritance makes them private.
Ans. Use the overall average formula. Multiply the national average by the total number of states to get total consumption, then subtract the sum of the given states. The remainder is Gujarat’s consumption. If no national average or total is given, Gujarat cannot be determined exactly, only estimated using comparable states or regional averages.
Ans. Use binary search on the eating speed from 1 to the largest pile, and return the smallest speed that is feasible. For a candidate speed, compute total hours as the sum of ceiling pile divided by speed. If hours are within h, try smaller. Time is O(n log maxPile), space is O(1).
Ans. Pick a situation where you stayed calm, protected the relationship, and moved the issue towards resolution. Emphasise listening without defensiveness, acknowledging frustration, clarifying the specific gaps, involving the right people, agreeing next steps, and following up. Interviewers listen for emotional control, accountability, professionalism, and a balance between client care and realistic boundaries.
Ans. SQL joins combine rows by a join condition: inner returns matches only, left returns all left rows plus matches, right returns all right rows plus matches, full returns all rows from both sides, and cross returns combinations. For outer joins, unmatched columns are filled with NULL. NULL join keys do not match each other unless handled explicitly.
Ans. Repeatedly divide the number by 62 and map each remainder to the Base-62 character set 0-9, A-Z, then a-z. Store the characters in a list or string builder, then reverse them because remainders are produced from least significant to most significant digit. Time complexity is O(log₆₂ n).
Ans. I would package the model as a versioned service, validate it offline, deploy it through CI/CD, release it gradually, and monitor it continuously. The key detail is observability: track latency, errors, prediction quality, data drift, and model drift, with alerts, rollback plans, audit logs, and a retraining process.
Ans. Open the box labelled “both” and take one fruit. Its label is wrong, so it cannot contain both; the fruit you pick shows whether it is the apple box or the orange box. Then use the fact that the other two labels are also wrong. If you picked an apple, the box labelled oranges is both, and the box labelled apples is oranges.
Ans. I would select the required columns from the main table and use an INNER JOIN to match rows in the related table on their shared key. For example, join orders to customers using customer_id. The important detail is the ON condition, because it defines which rows are related and prevents accidental Cartesian products.
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. ACID properties are guarantees that make database transactions reliable: Atomicity, Consistency, Isolation, and Durability. Atomicity means all changes commit or none do. Consistency keeps data valid under rules and constraints. Isolation makes concurrent transactions behave safely. Durability means committed changes survive crashes, usually through logging and persistent storage.
Ans. Runtime polymorphism in Java means the method that runs is chosen at runtime based on the actual object type, not the reference type. It is mainly achieved through method overriding, where a subclass provides its own implementation of a superclass or interface method. This enables flexible, extensible code.
Ans. An event listener in JavaScript is a function registered to run when a specific event happens, such as a click, key press, or page load. It is usually attached with addEventListener to an element, document, or window, and receives an event object with details about what occurred.
Ans. Scan the array once while keeping two variables: largest and second largest. For each element, update largest if it is bigger, shifting the old largest to second largest; otherwise update second largest if it lies between them. This uses constant extra space and runs in linear time. Handle duplicates based on whether “second largest” means distinct.
Ans. A strong answer should show that teamwork improves results through shared ideas, complementary skills, faster problem solving and mutual support. Pick a real situation where the team achieved more than one person could alone. Emphasise your contribution, how you listened, handled differences, supported others and helped deliver a clear outcome.
Ans. Hashing maps data to a fixed-size value, usually to store or find items quickly in a hash table. It should be used when you need fast lookup, insertion, or deletion by key, such as dictionaries, sets, caches, or duplicate detection. The key detail is handling collisions correctly.
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. chmod 777 gives read, write and execute permission to everyone: the file owner, the group and all other users. The three digits are octal permission values, where 7 means 4 plus 2 plus 1. It is usually unsafe for shared systems because anyone can modify or run the file.
Ans. Choose a specific COVID-19 example, such as public health messaging, remote community support, or misinformation management. Emphasise both benefits and risks: speed, reach, engagement, anxiety, and false information. Interviewers listen for balanced judgement, evidence-based thinking, empathy, adaptability, and an understanding of how communication choices affect public trust and behaviour.
Ans. The main types of machine learning are supervised learning, unsupervised learning, semi-supervised learning and reinforcement learning. Supervised learning uses labelled data, unsupervised learning finds patterns in unlabelled data, semi-supervised learning combines both, and reinforcement learning trains an agent to make decisions using rewards and penalties.
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. 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.
No question matches those filters. Reset filters.
Showing 59 of 106 questions. Ranked by how often the same question came back across interviews.
A spoken interview built from these questions, scored when you finish; the feedback is yours.
Start practisingWhen you are ready, record The One: a single interview hiring teams watch, so you stop repeating first rounds.
Candidate interviews most often cover CS fundamentals (54%) and DSA (26%).
Candidate interviews show an average of 3.6 rounds per experience, with a typical sequence of Online test → Group discussion → Technical → HR. Individual interview paths can vary.
Among questions with a recorded difficulty, the mix is easy 52%, medium 47%, hard 1%.
