BrowserStack Coding Interview Questions: OA, Machine Coding & Technical Interview
BrowserStack is an Indian product company headquartered in Mumbai, known for one of the most selective and distinctive hiring processes among Indian product companies. Unlike most companies that lean almost entirely on algorithmic DSA rounds, BrowserStack weighs machine coding rounds, where you build a real, working mini system, just as heavily as pure problem solving.
This guide is organized by interview stage, online assessment, machine coding, and technical interview, based on questions actually reported by candidates. Every algorithmic problem includes the exact question, a worked example, the right approach, and time or space complexity, while the machine coding tasks are presented as the system requirement briefs candidates actually received.
BrowserStack's Hiring Process for Fresher Roles
1. Application and Eligibility
- B.E./B.Tech, hired mainly through an annual campus drive, typically around August, often starting as a 6 month intern with conversion to full time based on performance.
- Apply through your college placement cell or BrowserStack's careers page for off campus openings.
2. Online Assessment (HackerEarth) 2 to 3 hours
- Exactly three problems worth 200 marks total, roughly 50 marks for an easy problem, 50 for a medium problem, and 100 for a hard, competitive programming style problem.
- A cutoff around 160 out of 200 has been reported. Quality and completeness on fewer problems matters more here than speed solving many easy ones.
3. Machine Coding Round 1 around 2 hours
- Build a real, working mini system rather than solving an algorithmic puzzle, evaluated on code quality, modularity, and how well you handle corner cases.
4. Machine Coding Round 2 around 2 to 3 hours
- A second, usually harder build task. Some variants explicitly ban using libraries like Selenium or WebDriver for browser automation tasks, forcing you to solve the underlying problem yourself.
5. Technical Interview With an Engineering Manager or Director
- A resume and project deep-dive combined with DSA, CS fundamentals, and systems questions such as scaling and caching.
6. HR or Hiring Manager Round
- Motivation, self awareness, and company fit questions.
Preparation Resources
Part 1 BrowserStack Online Assessment (OA) Questions
The OA runs on HackerEarth, 2 to 3 hours, exactly three problems scored out of 200 total, with difficulty escalating from easy to hard.
1. Spiral Sort Check Easy
Given an array, determine whether it satisfies a zigzag or spiral ordering, where arr[0] <= arr[n-1] <= arr[1] <= arr[n-2] and so on, alternating between the front and back of the array.
Input: arr = [1, 4, 2, 3]
Output: true
Why: arr[0]=1 <= arr[3]=3 <= arr[1]=4 <= arr[2]=2 fails, so check the exact
alternating condition defined by the problem carefully before coding
Approach: Use two pointers, one starting from the front and one from the back, and walk them inward while checking the required alternating inequality at each step. Return false the moment a check fails.
Complexity: Time O(n) · Space O(1)
Follow-up: How would you rearrange an arbitrary array into a valid spiral order instead of just checking one?
2. Adjacent Repetition String Filter Medium
Given a string and a target integer, remove every run of adjacent identical characters whose length exactly equals the target, leaving the rest of the string untouched.
Input: s = "aaabbcdd", target = 2
Output: "aaac"
Why: "bb" and "dd" are runs of length exactly 2 and are removed
Approach: Scan the string and group it into runs of consecutive identical characters. Keep a run in the output only if its length does not equal the target, then concatenate the surviving runs back together.
Complexity: Time O(n) · Space O(n)
Follow-up: What if removing a run could cause two previously separated runs to merge and now also qualify for removal?
3. Move All Zeros to the Start of an Array Easy
Given an array, move all zeros to the start of the array in a single pass, using constant extra space, while keeping the relative order of the non zero elements.
Input: arr = [1, 0, 2, 0, 3]
Output: [0, 0, 1, 2, 3]
Approach: Walk the array from the end, placing non zero elements from the back of a write pointer moving right to left, then fill the remaining front positions with zeros once all non zero elements are placed.
Complexity: Time O(n) · Space O(1)
Follow-up: How would you adapt this to move all zeros to the end instead, while still using only one pass?
4. JSON Field Diff Easy
Given two JSON objects with the same set of fields, output the names of every field whose value differs between the two objects.
Input: a = {"x": 1, "y": 2}, b = {"x": 1, "y": 5}
Output: ["y"]
Approach: Parse both objects into key value maps, then iterate over the keys of one map, comparing each value against the corresponding value in the other map, collecting the keys where they differ.
Complexity: Time O(n) where n is the number of fields · Space O(n)
Follow-up: How would you handle nested JSON objects, where a field's value is itself an object?
5. Number to Letter Mapping, Smallest String Medium
Given a mapping where 1 maps to 'a', 2 to 'b', up to 26 mapping to 'z', and a string of digits, find the lexicographically smallest string of letters that the digits could represent, splitting the digits into valid one or two digit groups.
Input: digits = "123"
Output: "aw"
Why: split as "1" -> a, "23" -> w, which is smaller than "1,2,3" -> "abc" compared lexicographically by the problem's rule
Approach: Work through the digit string greedily or with dynamic programming, at each position deciding whether to take one digit or two digits as the next letter, preferring whichever choice leads to the lexicographically smaller result down the line.
Complexity: Time O(n) · Space O(n)
Follow-up: How would you extend this to also return the count of all valid letter strings the digits could represent, not just the smallest?
6. Comment Remover Easy
Given a block of source code as a string, remove all single line // comments and multi line /* */ comments, while correctly leaving comment-like sequences inside string literals untouched.
Input: code with "// this is a comment" and a string literal containing "//not a comment"
Output: the code with real comments stripped but string literal contents preserved
Approach: Scan character by character, tracking whether you are currently inside a string literal, a single line comment, or a multi line comment, and only strip characters when you are inside an actual comment state, not inside a string literal.
Complexity: Time O(n) · Space O(n)
Follow-up: How would you handle nested multi line comments, if the language allowed them?
7. Design a Reverse Proxy With Health Aware Load Balancing Hard
Given N backend server addresses and M incoming requests to a set of endpoints, design a reverse proxy that forwards each request to a backend server using round robin load balancing, while monitoring server health and skipping servers currently marked as down.
Discussion points: how round robin state is tracked across requests, how server
health is checked and updated, and what happens when a request arrives while every
server is marked down
Approach: Maintain a list of servers with their current health status and a rotating pointer for round robin selection. On each incoming request, advance the pointer to the next healthy server, skipping any marked down, and forward the request there. Periodically or on failure, update each server's health status based on ping or response checks.
Complexity: Time O(1) amortized per request for server selection · Space O(N) for tracking server state
Follow-up: How would you extend this to weighted round robin, where some servers should receive proportionally more traffic than others?
Part 2 BrowserStack Machine Coding Rounds
Machine coding rounds at BrowserStack ask you to build a real, working system from scratch, not solve an algorithmic puzzle. You are evaluated on code quality, modularity, test coverage, and how you handle edge cases, not just whether the happy path works. Reported tasks include the following.
8. Build a tail -f Style Log Streaming Service
Brief:
Build a server side service that watches a log file and streams new lines to a connected web client in real time as they are written, similar to the Unix tail -f command. On initial connection, the client should immediately see the last 10 lines of the file. The service must support multiple simultaneous clients without retransmitting the entire file to each one.
What is evaluated:
- Correctly detecting new lines appended to the file without polling the entire file repeatedly
- Clean separation between the file watching logic and the client streaming logic
- Handling multiple clients connecting and disconnecting cleanly
- Reasonable behavior if the log file is rotated or truncated while being watched
9. Build a Stateless Browser Control Web Service
Brief: Build a web service exposing endpoints such as start, stop, cleanup, and get current URL, that controls a browser instance. Some variants explicitly disallow using Selenium or WebDriver, requiring you to implement the control logic yourself, for example by reading the browser's local history store directly rather than relying on a browser automation library.
What is evaluated:
- Genuine problem solving rather than wrapping an existing automation library
- Clean API design across the exposed endpoints
- Handling concurrent requests and cleanup correctly so browser instances do not leak
- Code organization and how you would extend the service to support additional browsers
10. Build an In-Memory Movie Knowledge Base With a CLI
Brief: Fetch data for a set of top movies, build an in-memory database linking movies to their cast, and provide a command line interface that lets a user query the top films for any given actor.
What is evaluated:
- Sensible in-memory data structure choices for fast lookups in both directions, movie to cast and actor to movies
- Clean CLI design and error handling for invalid queries
- Code that is easy to extend, for example to add new query types later
Part 3 BrowserStack Technical Interview Questions
The technical interview with an engineering manager or director covers DSA, systems thinking, and a deep dive into your projects.
Systems and CS Fundamentals Focus Areas
Real questions reported by candidates in the technical interview round:
- Given a 1TB file and only 8GB of RAM available, how would you process or analyze it.
- How would you count word frequency across a very large file that does not fit in memory.
- How did you find the last N lines of a log file efficiently, as a follow-up to the tail -f machine coding task.
- What is the difference between HTTP and HTTPS.
- What are common HTTP status and error codes, and what do they signify.
- What is the purpose of the User-Agent header in an HTTP request.
- What are common strategies for scaling a database as traffic grows.
- What logging strategy would you use for a production system, and why.
- What caching strategies would you consider for a high traffic system.
- When would you choose SQL over NoSQL, or the reverse.
- Explain the MapReduce programming model and when it is applicable.
- What strategies exist to prevent deadlocks in an operating system.
- Walk through your favourite or most challenging project, and explain how you would handle a late requirement change to it.
HR Interview Tips
The HR or hiring manager round checks motivation and self awareness. Common questions include:
- Tell me about yourself.
- What do you know about BrowserStack and what the product actually does.
- Where do you see yourself in five years.
- What are your strengths and weaknesses.
- Do you use GitHub, and do you take part in competitive programming contests.
- How did you first come to know about BrowserStack.
- What has your experience with the interview process been like so far.
Preparation Tips
- Do not treat this like a pure DSA interview. BrowserStack weighs machine coding, actually building a working system, as heavily as algorithmic problem solving, so practice building small real projects end to end, not just solving isolated LeetCode problems.
- Practice writing modular, testable code under time pressure. Machine coding rounds are evaluated on code quality and edge case handling, not just whether the demo works once.
- Get comfortable with systems level thinking. Questions about processing huge files with limited memory, caching, and scaling come up often, even for fresher roles.
- Know the product. BrowserStack interviewers consistently ask what you know about the company and its product, so spend real time understanding what BrowserStack actually does before your interview.
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