Head Digital Works Front end Developer Interview Questions and Answers

First round was a coding question with html, css, javascript to create 5 clickable boxes, change it's colors on click and update count

Round duration - 45 Minutes
Round difficulty - Easy

Q1. 
Triplets with Given Sum Problem
Given an array or list ARR consisting of N integers, your task is to identify all distinct triplets within the array that sum up to a specified number K.
Explanation:
A t...read more
Ans. 
The task is to identify all distinct triplets within an array that sum up to a specified number.
• Iterate through the array and use nested loops to find all possible triplets.

• Check if the sum of the triplet equals the specified number.

• Print the valid triplets or return -1 if no such triplet exists.
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Q2. 
Find Magic Index in Sorted Array
Given a sorted array A consisting of N integers, your task is to find the magic index in the given array, where the magic index is defined as an index i such that A[i] = i...read more
Ans. 
Find the magic index in a sorted array where A[i] = i.
• Iterate through the array and check if A[i] = i for each index i.

• Since the array is sorted, you can optimize the search using binary search.

• Return the index if found, else return -1.
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Round duration - 50 Minutes
Round difficulty - Hard

Q1. 
Alien Dictionary Problem Statement
You are provided with a sorted dictionary (by lexical order) in an alien language. Your task is to determine the character order of the alien language from this dictiona...read more
Ans. 
Given a sorted alien dictionary in an array of strings, determine the character order of the alien language.
• Iterate through the words in the dictionary to build a graph of character dependencies.

• Perform a topological sort on the graph to determine the character order.

• Return the character array representing the order of characters in the alien language.
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Q2. 
Jumping Numbers Problem Statement
Given a positive integer N, your goal is to find all the Jumping Numbers that are smaller than or equal to N.
A Jumping Number is one where every adjacent digit has an a...read more
Ans. 
Find all Jumping Numbers smaller than or equal to a given positive integer N.
• Iterate through numbers from 0 to N and check if each number is a Jumping Number.

• For each number, check if the absolute difference between adjacent digits is 1.

• Include all single-digit numbers as Jumping Numbers.

• Output the list of Jumping Numbers that are smaller than or equal to N.
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Q3. 
Matching Prefix Problem Statement
Given an integer N representing the number of strings in an array Arr composed of lowercase English alphabets, determine a string S of length N such that it can be used t...read more
Ans. 
Given an array of strings, find the lexicographically smallest string that can be used as a prefix to minimize the total cost of deleting prefixes from the strings.
• Iterate through the array to find the common prefix among all strings

• Choose the lexicographically smallest common prefix

• Delete the common prefix from each string in the array to minimize the total cost
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Round duration - 20 Minutes
Round difficulty - Easy

Q1. Questions on optimizations
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Q2. Question on React Js
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Medium level DSA question in JS

Q1. Asked about fundamentals of javascript and react
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Q2. React lifecycle in functional components
Ans. 
React lifecycle in functional components
• useEffect hook replaces lifecycle methods

• useEffect runs after every render by default

• useEffect can be controlled by dependencies array

• useEffect cleanup function can be used to clean up effects

• useLayoutEffect hook runs synchronously after DOM mutations
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Return numbers in array equal to sum

Round duration - 65 minutes
Round difficulty - Easy

There were 2 sections – 
Aptitude and Logical Reasoning and MCQ based on Java question ,C++, coding for 20 min and 45 min respectively.
Section A- Not very difficult to clear this round although less time was a problem.
Section B- It contains 15 multiple choice question on c/c++,java and 4 simple coding questions

Q1. 
Cycle Detection in a Singly Linked List
Determine if a given singly linked list of integers forms a cycle or not.
A cycle in a linked list occurs when a node's next points back to a previous node in the ...read more
Ans. 
Detect if a singly linked list forms a cycle by checking if a node's next pointer points back to a previous node.
• Traverse the linked list using two pointers, one moving at double the speed of the other.

• If the two pointers meet at any point, there is a cycle in the linked list.

• Use Floyd's Cycle Detection Algorithm for O(N) time complexity and O(1) space complexity.
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Round duration - 75 minutes
Round difficulty - Medium

It was an online coding test in which 3 coding question were given.

Q1. 
Smallest Window Problem Statement
Given two strings, S and X, your task is to find the smallest substring in S that contains all the characters present in X.
Example:
Input:
S = "abdd", X = "bd"
Outpu...read more
Ans. 
Find the smallest substring in string S that contains all characters in string X.
• Iterate through string S and keep track of characters in X found in a window

• Use two pointers to maintain the window and slide it to find the smallest window

• Return the smallest window containing all characters in X
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Q2. 
Smallest Integer Not Representable as Subset Sum
Given a non-decreasing sorted array ARR of N positive numbers, determine the smallest positive integer that cannot be expressed as the sum of elements from...read more
Ans. 
Find the smallest positive integer that cannot be expressed as the sum of elements from any proper subset of a non-decreasing sorted array of positive numbers.
• Start with the smallest possible integer that cannot be represented, which is 1.

• Iterate through the array and update the smallest integer that cannot be represented.

• If the current element is greater than the smallest integer that cannot be represented, return tha...read more
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Q3. 
Minimum Steps for a Knight to Reach Target
Given a square chessboard of size 'N x N', determine the minimum number of moves a Knight requires to reach a specified target position from its initial position...read more
Ans. 
Calculate the minimum number of moves a Knight needs to reach a target position on a chessboard.
• Implement a function that takes knight's starting position, target position, and chessboard size as input

• Use breadth-first search algorithm to find the shortest path for the Knight

• Consider all possible 8 movements of the Knight on the chessboard

• Return the minimum number of moves required for the Knight to reach the target po
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Round duration - 60 minutes
Round difficulty - Easy

It started with a discussion on the programs given in coding round. They asked me about my interest field after that they directly jumped into Networking, Linux and Ethical Hacking part looking my interest domain. They asked me various question on networking and linux.
Then they asked me to code a simple c program

Q1. 
Reverse Linked List Problem Statement
Given a singly linked list of integers, return the head of the reversed linked list.
Example:
Initial linked list: 1 -> 2 -> 3 -> 4 -> NULL
Reversed link...read more
Ans. 
Reverse a singly linked list of integers and return the head of the reversed linked list.
• Iterate through the linked list and reverse the pointers to point to the previous node.

• Keep track of the current, previous, and next nodes while reversing the linked list.

• Update the head of the reversed linked list as the last node encountered during reversal.
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Q2. What are the port numbers of protocols such as FTP and SMTP?
Ans. 
FTP uses port number 21 and SMTP uses port number 25.
• FTP uses port 21 for data transfer and port 20 for control information.

• SMTP uses port 25 for email communication.

• Understanding port numbers is important for network communication.
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Q3. Can you explain the OSI Model?
Ans. 
The OSI Model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven layers.
• The OSI Model stands for Open Systems Interconnection Model.

• It consists of seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.

• Each layer has specific functions and communicates with the adjacent layers.

• Example: Layer 1 (Physical) deals with physi...read more
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Q4. How do you copy files in Linux?
Ans. 
To copy files in Linux, you can use the 'cp' command.
• Use the 'cp' command followed by the source file and destination directory to copy a file.

• To copy a directory and its contents, use the '-r' flag with the 'cp' command.

• You can also use wildcards like '*' to copy multiple files at once.
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Round duration - 60 minutes
Round difficulty - Easy

Technical round with 3 problems based on DSA and Algorithms.

Q1. 
Smallest Integer Not Representable as Subset Sum
Given a non-decreasing sorted array ARR of N positive numbers, determine the smallest positive integer that cannot be expressed as the sum of elements from...read more
Ans. 
Find the smallest positive integer that cannot be expressed as the sum of elements from any proper subset of a given array.
• Sort the array in non-decreasing order.

• Iterate through the array and keep track of the smallest sum that can be formed.

• If the next element in the array is greater than the current sum + 1, then the answer is the current sum + 1.

• Return the answer as the smallest integer not representable as a subset
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Q2. 
Reverse Linked List Problem Statement
Given a singly linked list of integers, return the head of the reversed linked list.
Example:
Initial linked list: 1 -> 2 -> 3 -> 4 -> NULL
Reversed link...read more
Ans. 
Reverse a singly linked list of integers and return the head of the reversed linked list.
• Iterate through the linked list and reverse the pointers to point to the previous node instead of the next node.

• Use three pointers to keep track of the current, previous, and next nodes while reversing the linked list.

• Update the head of the reversed linked list to be the last node encountered during the reversal process.
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Q3. 
Smallest Window Problem Statement
Given two strings S and X containing random characters, the task is to find the smallest substring in S which contains all the characters present in X.
Input:
The first...read more
Ans. 
The task is to find the smallest substring in string S which contains all the characters present in string X.
• Iterate through string S and keep track of characters in X using a hashmap

• Use two pointers to maintain a sliding window and find the smallest window containing all characters in X

• Return the smallest window found
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Round duration - 60 minutes
Round difficulty - Easy

Technical round with questions based on OOPS and Angular.

Q1. What are the different OOP concepts?
Ans. 
OOP concepts include inheritance, encapsulation, polymorphism, and abstraction.
• Inheritance allows a class to inherit properties and behavior from another class.

• Encapsulation restricts access to certain components of an object, protecting its integrity.

• Polymorphism allows objects to be treated as instances of their parent class.

• Abstraction hides the complex implementation details of an object and only shows the necessar
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Round duration - 60 minutes
Round difficulty - Easy

Questions based on System Design, ajax, jquery were asked.

Q1. How would you design a traffic light system?
Ans. 
Designing a traffic light system involves creating a system that controls the flow of traffic at intersections.
• Divide the traffic light system into three main lights: red, yellow, and green.

• Implement timers to control the duration of each light.

• Include sensors to detect the presence of vehicles and pedestrians.

• Consider implementing a pedestrian crossing signal.

• Integrate a central control system to coordinate the timing
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Q2. How does AJAX work?
Ans. 
AJAX allows for asynchronous communication between client and server without needing to reload the entire page.
• AJAX stands for Asynchronous JavaScript and XML.

• It allows for sending and receiving data from a server without reloading the entire page.

• AJAX uses XMLHttpRequest object to make requests to the server.

• It can update parts of a web page without requiring a full page reload.

• Commonly used in web applications to pro
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Q3. What is the difference between AngularJS and jQuery?
Ans. 
AngularJS is a full-fledged MVC framework for building dynamic web applications, while jQuery is a lightweight library for DOM manipulation and event handling.
• AngularJS is a full-fledged MVC framework, providing features like two-way data binding, dependency injection, and routing.

• jQuery is a lightweight library primarily used for DOM manipulation and event handling.

• AngularJS is suitable for building single-page applic...read more
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