Toptal Senior Software Engineer Interview Questions and Answers

Q1. DS and algorithm questions
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Q1. IOS /Skillset questions some tricky questions
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Q1. Personality and Compensation discussion
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Q1. Asked to write a program to check whether string is valid or not. String consists of only three kind of special characters "(), [], {}". We need to return true if all special characters are in correct for...read more
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Q2. What is useRef hook used for?
Ans. 
useRef hook is used to persist a mutable value across renders without causing a re-render.
• Used to store mutable values that do not trigger re-renders.

• Commonly used for accessing DOM elements or storing previous values.

• Does not cause a re-render when the value changes.
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Q3. What are the best practices to avoid rerenders and to improve performance
Ans. 
Use memoization, virtual DOM, and shouldComponentUpdate to avoid unnecessary rerenders and improve performance.
• Implement memoization to store the result of expensive function calls and avoid recalculating them.

• Use virtual DOM to efficiently update only the parts of the UI that have changed.

• Override shouldComponentUpdate to prevent unnecessary rerenders by comparing current and next props/state.
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Q4. What are callbacks, Promises, async await
Ans. 
Callbacks, Promises, async await are asynchronous programming concepts in JavaScript.
• Callbacks are functions passed as arguments to another function to be executed later.

• Promises are objects representing the eventual completion or failure of an asynchronous operation.

• async await is a syntax for writing asynchronous code that looks synchronous, making it easier to read and maintain.

• Example: Using a callback to handle th...read more
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Q1. Introduction. Questions related to OOPS concepts, MVC
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Round duration - 20 minutes
Round difficulty - Easy

50 Logical ability, mathematical and image patterns questions are to be done in 20 minutes. A minimum cutoff has to be cleared. (ask your recruiter)
Tip – majority questions are of image pattern, so try to solve those first as they take lesser time

Round duration - 90 minutes
Round difficulty - Easy

Q1. 
Secret Message Decoding Problem
Ninja encountered an encoded secret message where each character from 'A' to 'Z' is mapped to a numeric value (A = 1, B = 2, ..., Z = 26). Given a numeric sequence (SEQ) de...read more
Ans. 
The problem involves decoding a numeric sequence back into a valid string based on a given mapping of characters to numeric values.
• Use dynamic programming to keep track of the number of ways to decode the sequence at each position.

• Consider edge cases such as '0' and '00' which do not have valid decodings.

• Handle cases where two digits can be combined to form a valid character (e.g., '12' corresponds to 'L').
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Q2. 
Digits Decoding Problem Statement
A few days back, Ninja encountered a string containing characters from ‘A’ to ‘Z’ which indicated a secret message. For security purposes, he encoded each character of th...read more
Ans. 
The problem involves decoding a numeric sequence into a valid string using a given mapping of characters to numbers.
• Use dynamic programming to count the number of ways to decode the sequence.

• Consider different cases for decoding single digits and pairs of digits.

• Keep track of the number of ways to decode at each position in the sequence.

• Return the final count modulo 10^9 + 7 as the answer.
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Round duration - 180 minutes
Round difficulty - Easy

Since I applied for senior frontend role (React), I was asked questions on following topics – Javascript (easy, medium, hard), HTML, HTML5 api, CSS, SVG, React (easy, medium, hard), UI/UX related
A very lengthy and tiring round.

Round duration - 20 minutes
Round difficulty - Easy

Round duration - 180 mins
Round difficulty - Medium

It was aptitude & english then coding round

Q1. 
Character Counting Challenge
Create a program that counts and prints the total number of specific character types from user input. Specifically, you need to count lowercase English alphabets, numeric digi...read more
Ans. 
Create a program to count lowercase alphabets, digits, and white spaces from user input until '$' is encountered.
• Read characters from input stream until '$' is encountered

• Count lowercase alphabets, digits, and white spaces separately

• Print the counts of each character type as three integers separated by spaces
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Round duration - 60 Minutes
Round difficulty - Easy

Online coding round 3 questions were there leetcode easy

Q1. 
Preorder Traversal Problem Statement
You are provided with the root node of a binary tree comprising N nodes. Your objective is to output its preorder traversal. Preorder traversal of a binary tree is per...read more
Ans. 
Implement a function to perform preorder traversal on a binary tree given the root node.
• Create a recursive function to traverse the tree in preorder fashion.

• Visit the root node, then recursively traverse left subtree, followed by right subtree.

• Store the visited nodes in an array and return the array as the result.

• Example: For the input tree [1, 2, 3, 4, -1, 5, 6, -1, 7, -1, -1, -1, -1, -1, -1], the preorder traversal o
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Round duration - 60 Minutes
Round difficulty - Easy

They tested my basic data structure knowledge

Q1. Can you explain the concept of static variables and classes in Object-Oriented Programming?
Ans. 
Static variables and classes in OOP are used to store data that is shared among all instances of a class.
• Static variables are shared among all instances of a class and retain their value throughout the program's execution.

• Static classes cannot be instantiated and are used to group related static members together.

• Example: In a class representing a bank account, a static variable could be used to store the total number o...read more
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Round duration - 60 Minutes
Round difficulty - Medium

It was more about technical knowledge and problem solving skills

Q1. Can you design a login page for Facebook?
Ans. 
I can design a login page for Facebook with user input fields for email/phone and password, a 'Login' button, and 'Forgot password?' link.
• Include user input fields for email/phone and password

• Add a 'Login' button for submitting credentials

• Include a 'Forgot password?' link for password recovery

• Design the page with Facebook branding and color scheme
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Round duration - 30 Minutes
Round difficulty - Easy

General question and CTC discussion

Q1. Can you discuss the CTC (Cost to Company) offered in this position?
Ans. 
The CTC offered for this position is competitive and includes salary, benefits, and bonuses.
• CTC includes salary, benefits, bonuses, and any other perks offered by the company.

• It is important to consider the overall compensation package, not just the base salary.

• Negotiation for a higher CTC may be possible based on experience and skills.

• Example: CTC for this position ranges from $100,000 to $120,000 per year.
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Q1. Tell me about yourself
Ans. 
I am a Senior Software Engineer with 8 years of experience in developing scalable and efficient software solutions.
• 8 years of experience in software development

• Expertise in developing scalable and efficient software solutions

• Proficient in programming languages such as Java, Python, and JavaScript

• Strong problem-solving skills and ability to work in a team environment
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Q1. Architecture discussion around projects
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Q1. Caching, auth discussion in depth
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