Testbook.com Senior Sdet Engineer Interview Questions and Answers

Round duration - 120 minutes
Round difficulty - Easy

It was a mix of mathematical aptitude, logical ability, and puzzles along with 2 programming questions of easy and medium level. Time was enough and no sectional time was present. 1-2 MCQs on SQL were also present.

This round was immediately followed by an SHL aptitude test which was basically a quick limited time check of your verbal ability and math because many questions were to be done in 1 hour.

Q1. 
Boolean Matrix Transformation Challenge
Given a 2-dimensional boolean matrix mat of size N x M, your task is to modify the matrix such that if any element is 1, set its entire row and column to 1. Specifi...read more
Ans. 
Modify a boolean matrix such that if any element is 1, set its entire row and column to 1.
• Iterate through the matrix and mark rows and columns to be modified

• Use additional arrays to keep track of rows and columns to be modified

• Update the matrix in-place based on the marked rows and columns
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Round duration - 60 minutes
Round difficulty - Easy

It was an online video interview round on HackerEarth with simultaneous code option. It was mostly justifying your resume in the first 15 minutes. After that OOPS was majorly asked. Basics of programming including questions on STL were asked. A class which required inheritance was asked by the interviewer to write. I was helped by the interviewer if i got stuck somewhere, Some questions on implementation of hashmaps and priority queues were also asked. A puzzle was asked which luckily struct to me at that moment.

Q1. Basics of js and react
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Q2. What are closures and give an example
Ans. 
Closures are functions that have access to variables from their outer scope even after the outer function has finished executing.
• Closures are created when a function is defined within another function and has access to the outer function's variables.

• They can access variables from the outer function even after the outer function has returned.

• Closures are commonly used in event handlers and callbacks in JavaScript.
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Q3. What is event loop and features of es5
Ans. 
Event loop is a mechanism that allows JavaScript to perform non-blocking operations by handling asynchronous events.
• Event loop is responsible for executing code, collecting and processing events, and executing queued sub-tasks.

• ES5 features include strict mode, JSON object, Array methods like forEach, map, filter, and reduce, and Object.create method.

• ES5 also introduced new methods for manipulating strings, such as trim
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Q1. General management round and past experience
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Q1. Explain request lifecycle in rails?
Ans. 
Request lifecycle in Rails involves routing, controller actions, rendering views, and responding to the client.
• 1. Request comes in through the browser or API endpoint.

• 2. Rails router determines which controller and action to route the request to.

• 3. Controller action processes the request, interacts with the model, and prepares data for the view.

• 4. View template is rendered with the data from the controller.

• 5. Response ...read more
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Q2. Code Merge Sort using Ruby
Ans. 
Implement Merge Sort algorithm in Ruby
• Divide the array into two halves recursively

• Merge the sorted halves back together

• Use a helper method to merge the two halves
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2.5 Hours 2 Coding que and sql query and topin tech platform

Q1. Based on boolean matrix
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Q2. Find k closest node of given given node in a BST.
Ans. 
Find k closest nodes to a given node in a BST.
• Perform an inorder traversal of the BST to get a sorted list of nodes.

• Use a priority queue to keep track of the k closest nodes based on their absolute difference with the target node.

• Populate the priority queue with the first k nodes from the inorder traversal.

• For each subsequent node, calculate its absolute difference with the target node and compare it with the top eleme...read more
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Q1. Check if string is palindrome
Ans. 
Check if a string is the same forwards and backwards
• Iterate through the string from both ends and compare characters

• Use built-in functions like reverse() to check for palindrome

• Ignore spaces and punctuation when checking for palindrome
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Python technical SQL basic

Two dynamic programming challenges at the hard level on LeetCode and 10 medium-level SQL challenge.

Q1. Question on Binary trees: if symmetric, easy string question using hashmap
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Q2. If we are hosting a live test how to show real time ranking, HLD for this and what algorithms can we use
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Q1. Database schema design for a feature where user can be free, gold, platinum.
Ans. 
Use a user table with a column for user type (free, gold, platinum)
• Create a user table with columns for user ID, name, email, user type

• Use a separate table for user types with columns for type ID and type name

• Establish a one-to-many relationship between user and user type tables

• Example: user table - user_id, name, email, type_id; user_type table - type_id, type_name
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Q1. HLD for live rank dashboard for a live test where millions of users are doing test
Ans. 
High-level design for a live rank dashboard for a live test with millions of users.
• Use a scalable architecture to handle millions of users concurrently.

• Implement real-time data processing to update ranks dynamically.

• Utilize caching mechanisms to improve performance and reduce load on the database.

• Design a user-friendly interface with intuitive data visualization.

• Include features for filtering, sorting, and searching to
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