Head Digital Works Front end Developer Interview Questions and Answers for Freshers

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

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 - 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

Round duration - 60 minutes
Round difficulty - Easy

Two coding questions were given in the first round to be solved in 60 minutes.

Q1. 
Rearrange Array Elements Problem Statement
Given an array A containing 'N' integers and an integer m, rearrange the elements of the array such that the differences between the array elements and m are sor...read more
Ans. 
Rearrange array elements based on their differences from a given integer.
• Calculate the differences between each element and the given integer.

• Sort the elements based on their differences while maintaining the original order for elements with the same difference.

• Implement a function to rearrange the array elements as per the given criteria.
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Q2. 
Print Nodes at Distance K from a Given Node
Given an arbitrary binary tree, a node of the tree, and an integer 'K', find all nodes that are at a distance K from the specified node, and return a list of th...read more
Ans. 
The task is to find all nodes in a binary tree that are at a distance K from a given node.
• Traverse the binary tree to find the given node

• From the given node, perform a depth-first search to find all nodes at distance K

• Use a list to store the values of the nodes at distance K

• Return the list of values in any order
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Round duration - 60 minutes
Round difficulty - Easy

This was a technical round with questions based on DSA, DBMS, Computer Networking and project based questions.

Q1. 
Triangle of Numbers Pattern
Ninja is tasked with printing a triangle pattern based on a given number 'N' for any test case.
Example:
Input:
N = 4
Output:
   1
  232
 34545
4567654
Explanation:
The pat...read more
Ans. 
Print a triangle pattern of numbers based on a given number 'N'.
• Iterate through each row and print the numbers accordingly

• Use spaces to center-align the numbers in each row

• Increment the numbers in each row as per the pattern
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Q2. What is the difference between a web server and an application server?
Ans. 
Web server serves static content over HTTP, while application server runs dynamic content and business logic.
• Web server handles HTTP requests and responses, serving static content like HTML, images, and CSS.

• Application server executes business logic, runs dynamic content, and interacts with databases.

• Web server examples include Apache, Nginx, while application server examples include Tomcat, JBoss.

• Web server focuses on...read more
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Q3. How does the internet work?
Ans. 
The internet is a global network of interconnected computers that communicate using standardized protocols.
• The internet is made up of a vast number of interconnected networks of computers.

• Data is transmitted over the internet using protocols such as TCP/IP.

• Websites are hosted on servers connected to the internet, and users access them using web browsers.

• Internet Service Providers (ISPs) provide access to the internet f...read more
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Q4. Write a SQL query to find the nth highest salary.
Ans. 
SQL query to find the nth highest salary
• Use the 'SELECT DISTINCT' statement to get unique salary values

• Order the salaries in descending order using 'ORDER BY' clause

• Use 'LIMIT' and 'OFFSET' to get the nth highest salary
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Round duration - 30 minutes
Round difficulty - Easy

Typical HR round with behavioral problems.

Round duration - 90 minutes
Round difficulty - Medium

Questions on aptitude, English, logical reasoning, C/C++ and 5 coding ques. (only pseudo code).

Q1. 
Minimum Jumps Problem Statement
Bob and his wife are in the famous 'Arcade' mall in the city of Berland. This mall has a unique way of moving between shops using trampolines. Each shop is laid out in a st...read more
Ans. 
Find the minimum number of trampoline jumps Bob needs to make to reach the final shop, or return -1 if it's impossible.
• Use Breadth First Search (BFS) algorithm to find the minimum number of jumps required.

• Keep track of the visited shops to avoid revisiting them.

• If a shop has an Arr value of 0, it is impossible to reach the final shop.

• Return -1 if the final shop cannot be reached.
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Q2. 
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 S that contains all characters in X.
• Use a sliding window approach to find the smallest window in S containing all characters of X.

• Maintain a hashmap to keep track of characters in X and their frequencies in the current window.

• Slide the window to the right, updating the hashmap and shrinking the window until all characters in X are present.

• Return the smallest window found.

• Example: S = 'abd
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Q3. 
Rat in a Maze Problem Statement
You need to determine all possible paths for a rat starting at position (0, 0) in a square maze to reach its destination at (N-1, N-1). The maze is represented as an N*N ma...read more
Ans. 
Find all possible paths for a rat in a maze from start to destination.
• Use backtracking to explore all possible paths in the maze.

• Keep track of visited cells to avoid revisiting them.

• Return paths in alphabetical order as a list of strings.
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Round duration - 60 minutes
Round difficulty - Easy

Questions based on OOPS were asked in this round.

Q1. What is a virtual function?
Ans. 
A virtual function is a function in a base class that is declared using the keyword 'virtual' and can be overridden by a function with the same signature in a derived class.
• Virtual functions allow for dynamic polymorphism in C++

• They are used in inheritance to achieve runtime polymorphism

• Virtual functions are declared in a base class and can be overridden in derived classes

• They are called based on the type of object bei...read more
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Q2. What are the types of polymorphism in Object-Oriented Programming?
Ans. 
Types of polymorphism in OOP include compile-time (method overloading) and runtime (method overriding) polymorphism.
• Compile-time polymorphism is achieved through method overloading, where multiple methods have the same name but different parameters.

• Runtime polymorphism is achieved through method overriding, where a subclass provides a specific implementation of a method that is already defined in its superclass.

• Polymor...read more
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Q3. What is the difference between deep copy and shallow copy?
Ans. 
Deep copy creates a new object and recursively copies all nested objects, while shallow copy creates a new object and copies only the references to nested objects.
• Deep copy creates a new object and copies all nested objects, while shallow copy creates a new object and copies only the references to nested objects.

• In deep copy, changes made to the original object do not affect the copied object, while in shallow copy, ch...read more
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Round duration - 30 minutes
Round difficulty - Easy

HR round with typical behavioral problems.