Worldline Full Stack Developer Interview Questions and Answers

Round duration - 90 Minutes
Round difficulty - Easy

MCQ based on web and oops.

Q1. 
Subtree of Another Tree Problem Statement
Given two binary trees, T and S, determine whether S is a subtree of T. The tree S should have the same structure and node values as a subtree of T.
Explanation:
...read more
Ans. 
Determine if one binary tree is a subtree of another binary tree based on their structure and node values.
• Traverse through the main tree and check if any subtree matches the second tree

• Use recursion to compare nodes of both trees

• Handle edge cases like empty trees or null nodes

• Check if the root node of the second tree exists in the main tree
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Round duration - 50 Minutes
Round difficulty - Easy

This round involved a discussion of a project I had undertaken recently and a coding problem. How does an Angular application work? List out differences between AngularJS and Angular

Q1. 
Count Ways to Reach the N-th Stair Problem Statement
You are provided with a number of stairs, and initially, you are located at the 0th stair. You need to reach the Nth stair, and you can climb one or tw...read more
Ans. 
The task is to find the number of distinct ways to climb from the 0th step to the Nth step, where each time you can climb either one step or two steps.
• Use dynamic programming to solve this problem

• Create an array to store the number of ways to reach each step

• Initialize the first two elements of the array as 1 and 2

• For each subsequent step, the number of ways to reach that step is the sum of the number of ways to reach t...read more
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Round duration - 80 Minutes
Round difficulty - Medium

The interview mostly focused on coding problems and Java-related concepts.

Q1. How is a Linked List implemented in Java, and when would you prefer it over an ArrayList?
Ans. 
A Linked List in Java is implemented using nodes with references to the next node. It is preferred over an ArrayList when frequent insertions and deletions are required.
• In Java, a Linked List is implemented using a Node class with data and a reference to the next Node.

• LinkedList class in Java provides methods like add(), remove(), and get() for manipulating the list.

• Linked List is preferred over ArrayList when frequent...read more
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Q2. 
Prerequisite Task Completion Verification
Given a positive integer 'N', representing the number of tasks, and a list of dependency pairs, determine if it is possible to complete all tasks considering thes...read more
Ans. 
Determine if it is possible to complete all tasks considering prerequisites.
• Create a graph representation of the tasks and dependencies.

• Use topological sorting to check if there is a cycle in the graph.

• Return 'Yes' if no cycle is found, 'No' otherwise.
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Q3. 
Kth Smallest and Largest Element Problem Statement
You are provided with an array 'Arr' containing 'N' distinct integers and a positive integer 'K'. Your task is to find the Kth smallest and Kth largest e...read more
Ans. 
Find the Kth smallest and largest elements in an array.
• Sort the array to easily find the Kth smallest and largest elements.

• Ensure K is within the array's size to avoid errors.

• Handle multiple test cases efficiently.

• Consider edge cases like when N is small or K is at the extremes.
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Round duration - 30 Minutes
Round difficulty - Easy

This was the Hiring Manager Round. What is a Primary Key? What is a Cross-Join? What is the difference between Clustered and Non-clustered index?

Q1. 
Search in a Row-wise and Column-wise Sorted Matrix Problem Statement
You are given an N * N matrix of integers where each row and each column is sorted in increasing order. Your task is to find the positi...read more
Ans. 
Given a sorted N * N matrix, find the position of a target integer 'X'.
• Iterate over rows and columns to search for the target integer 'X'.

• Utilize the sorted nature of the matrix to optimize the search process.

• Return the position of 'X' if found, else return '-1 -1'.
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Round duration - 70 minutes
Round difficulty - Medium

The test started around 3 pm and was of 70 minutes. 3 coding questions were asked which were mainly on trees and number theory.

Q1. 
Factorial Calculation Problem Statement
Develop a program to compute the factorial of a given integer 'n'.
The factorial of a non-negative integer 'n', denoted as n!, is the product of all positive integ...read more
Ans. 
Program to compute factorial of a given integer 'n', with error handling for negative values.
• Create a function to calculate factorial using a loop or recursion

• Check if input is negative, return 'Error' if true

• Handle edge cases like 0 and 1 separately

• Return the calculated factorial value
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Q2. 
Next Greater Element Problem Statement
Given a list of integers of size N, your task is to determine the Next Greater Element (NGE) for every element. The Next Greater Element for an element X is the firs...read more
Ans. 
The task is to find the Next Greater Element for each element in a list of integers.
• Iterate through the list of integers from right to left

• Use a stack to keep track of elements whose NGE is yet to be found

• Pop elements from the stack until a greater element is found or the stack is empty

• Assign the NGE as the top element of the stack or -1 if the stack is empty
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Q3. 
Ceil Value from BST Problem Statement
Given a Binary Search Tree (BST) and an integer, write a function to return the ceil value of a particular key in the BST.
The ceil of an integer is defined as the s...read more
Ans. 
Ceil value of a key in a Binary Search Tree (BST) is the smallest integer greater than or equal to the given number.
• Traverse the BST to find the closest integer greater than or equal to the given key.

• Compare the key with the current node value and update the ceil value accordingly.

• Recursively traverse left or right subtree based on the key value to find the ceil value.

• Return the ceil value once found for each test case
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Round duration - 60 minutes
Round difficulty - Medium

Interviewer was very friendly and supportive. My interview happened on google meet. What is a View? What is Denormalization? Difference between “==” and “===” operators in js.

Q1. 
Sub Sort Problem Statement
You are given an integer array ARR. Determine the length of the shortest contiguous subarray which, when sorted in ascending order, results in the entire array being sorted in a...read more
Ans. 
Determine the length of the shortest contiguous subarray that needs to be sorted to make the entire array sorted in ascending order.
• Iterate from left to right to find the first element out of order.

• Iterate from right to left to find the last element out of order.

• Calculate the length of the subarray between the two out of order elements.
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Q2. 
Sort 0 1 2 Problem Statement
Given an integer array arr of size 'N' containing only 0s, 1s, and 2s, write an algorithm to sort the array.
Input:
The first line contains an integer 'T' representing the n...read more
Ans. 
Sort an integer array containing only 0s, 1s, and 2s in linear time complexity.
• Use three pointers to keep track of 0s, 1s, and 2s while traversing the array.

• Swap elements based on the values encountered to sort the array in-place.

• Time complexity should be O(N) to solve the problem efficiently.
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Round duration - 60 minutes
Round difficulty - Medium

What are some of the advantages of Angular over other frameworks?

Q1. 
Cousin Nodes in a Binary Tree
Determine if two nodes in a binary tree are cousins. Nodes are considered cousins if they are at the same level and have different parents.
Explanation:
In a binary tree, e...read more
Ans. 
Determine if two nodes in a binary tree are cousins based on level and parent nodes.
• Traverse the binary tree to find the levels and parents of the given nodes.

• Check if the nodes are at the same level and have different parents to determine if they are cousins.

• Return 'YES' if the nodes are cousins, 'NO' otherwise.

• Example: For input '1 2 3 4 -1 5 6 -1 7 -1 -1 -1 -1 -1 -1' and nodes 4 7, output is 'YES'.
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Round duration - 10 minutes
Round difficulty - Easy

I got a call from HR in the evening around 6:30 pm.

Q1. Can you tell me about yourself?
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Q2. How was your experience with the previous two technical rounds?
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Q3. What do you know about Paytm?
Ans. 
Paytm is a leading Indian digital payment platform offering a wide range of services including mobile recharges, bill payments, and online shopping.
• Founded in 2010 by Vijay Shekhar Sharma

• Offers services like mobile recharges, bill payments, online shopping, and digital wallet

• Acquired by One97 Communications in 2013

• Expanded into financial services like Paytm Payments Bank and Paytm Money

• One of the largest digital paymen
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Round duration - 70 minutes
Round difficulty - Easy

there was some coding questions and some mcqs related to js, html, css, java and aptitude.

Q1. 
Bridge in Graph Problem Statement
Given an undirected graph with V vertices and E edges, your task is to find all the bridges in this graph. A bridge is an edge that, when removed, increases the number of...read more
Ans. 
Find all the bridges in an undirected graph by identifying edges that, when removed, increase the number of connected components.
• Use Tarjan's algorithm to find bridges in the graph.

• Keep track of the discovery time and low time of each vertex during DFS traversal.

• An edge (u, v) is a bridge if low[v] > disc[u].

• Handle multiple test cases efficiently to find bridges in each graph.

• Ensure the output contains the count of
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Q2. 
House Robber Problem Statement
Mr. X is a professional robber with a plan to rob houses arranged in a circular street. Each house has a certain amount of money hidden, separated by a security system that ...read more
Ans. 
The task is to find the maximum amount of money Mr. X can rob from houses arranged in a circle without alerting the police.
• The problem can be solved using dynamic programming.

• Create two arrays to store the maximum amount of money robbed when considering the first house and when not considering the first house.

• Iterate through the array and update the maximum amount of money robbed at each house.

• The final answer will be
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Round duration - 60 Minutes
Round difficulty - Medium

This round had questions mainly from Java 8 and its important features followed by some questions from Spring Boot.

Q1. What are Java 8 streams?
Ans. 
Java 8 streams are a sequence of elements that can be processed in parallel or sequentially.
• Streams provide a functional programming approach to process collections in Java.

• They allow for concise and expressive code.

• Streams can be used to filter, map, reduce, and perform other operations on data.

• Example: List numbers = Arrays.asList(1, 2, 3, 4, 5); numbers.stream().filter(n -> n % 2 == 0).forEach(System.out::println);

• T...read more
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Q2. Write a Java 8 program to iterate through a Stream using the forEach method.
Ans. 
A Java 8 program to iterate a Stream using the forEach method.
• Create a Stream object from a collection or array

• Use the forEach method to perform an action on each element of the Stream

• The action can be a lambda expression or a method reference
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Q3. How does Spring Boot work?
Ans. 
Spring Boot is a framework that simplifies the development of Java applications by providing default configurations and dependencies.
• Spring Boot eliminates the need for manual configuration by providing sensible defaults.

• It uses an embedded server, such as Tomcat or Jetty, to run the application.

• Spring Boot automatically configures the application based on the dependencies added to the project.

• It promotes convention ov...read more
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Q4. What is dependency injection?
Ans. 
Dependency Injection is a design pattern where the dependencies of a class are provided externally rather than being created within the class itself.
• Dependency Injection helps in achieving loose coupling between classes.

• It allows for easier testing and maintenance of code.

• In Spring Boot, dependencies are injected using annotations like @Autowired.

• Example: In a Spring Boot application, if a class requires a database con...read more
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Q5. Can you explain the @RestController annotation in Spring Boot?
Ans. 
The @RestController annotation in Spring Boot is used to mark a class as a RESTful controller.
• It combines the @Controller and @ResponseBody annotations.

• It eliminates the need for annotating each method with @ResponseBody.

• It automatically serializes the return value of the methods into JSON/XML response.

• It is commonly used to build RESTful web services in Spring Boot.
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Q6. What are the different methods of session management in Servlets?
Ans. 
Different methods of session management in Servlet
• Cookies

• URL Rewriting

• Hidden Form Fields

• Session Tracking API

• HTTP Session
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Round duration - 60 Minutes
Round difficulty - Medium

This was a preety much mixed round ranging questions from Java , MVC to DBMS , Web Security and API Design. More emphasis was given on the fundamentals of the subject rather than the advanced topics.

Q1. What is CORS in MVC and how does it work?
Ans. 
CORS in MVC is Cross-Origin Resource Sharing, a mechanism that allows restricted resources on a web page to be requested from another domain.
• CORS is a security feature implemented in web browsers to prevent cross-origin requests by default.

• It works by adding specific HTTP headers to the server's response, indicating which origins are allowed to access the resources.

• In MVC, CORS can be configured using the 'EnableCors' ...read more
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Q2. Can you explain in brief the role of different MVC components?
Ans. 
MVC components include Model, View, and Controller. Model represents data and business logic, View displays the data, and Controller handles user input and updates the Model and View.
• Model: Represents data and business logic

• View: Displays the data to the user

• Controller: Handles user input and updates the Model and View
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Q3. What is the difference between a clustered index and a non-clustered index?
Ans. 
Clustered index determines the physical order of data in a table, while non-clustered index has a separate structure.
• Clustered index determines the physical order of data in a table

• Non-clustered index has a separate structure that includes a copy of the indexed columns and a pointer to the actual data

• A table can have only one clustered index, but multiple non-clustered indexes

• Clustered index is faster for retrieving la...read more
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Q4. What is SQL injection?
Ans. 
SQL injection is a web security vulnerability that allows an attacker to manipulate a database query to execute unauthorized actions.
• SQL injection occurs when user-supplied data is not properly validated or sanitized before being used in an SQL query.

• Attackers can exploit this vulnerability to bypass authentication, retrieve sensitive data, modify or delete data, or even execute arbitrary commands.

• To prevent SQL inject...read more
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Q5. What are the advantages of web services?
Ans. 
Web services offer advantages such as interoperability, scalability, reusability, and platform independence.
• Interoperability: Web services allow different applications to communicate and share data regardless of the programming languages or platforms they are built on.

• Scalability: Web services can handle a large number of requests and can be easily scaled up or down to meet changing demands.

• Reusability: Web services pr...read more
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Round duration - 45 Minutes
Round difficulty - Medium

This round started with some questions from Frontend Web Development primarily from HTML and CSS followed by some questions from DevOps and Git. The interviewer was quite satisfied by my answers and overall this round went preety well.

Q1. How can you optimize the loading of website assets?
Ans. 
Optimize website assets loading by minimizing file sizes, leveraging caching, and using asynchronous loading.
• Minimize file sizes by compressing images, minifying CSS and JavaScript files

• Leverage caching by setting appropriate cache headers and using a content delivery network (CDN)

• Use asynchronous loading techniques such as lazy loading, deferred loading, and async/defer attributes

• Combine and bundle multiple files to r...read more
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Q2. What are the new tags for media elements introduced in HTML5?
Ans. 
New tags in Media Elements in HTML5 include <audio> and <video>.
• <audio> tag for audio content

• <video> tag for video content

• Attributes like controls, autoplay, loop, etc. can be used with these tags
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Q3. Can you explain a use case for Docker?
Ans. 
Docker is a containerization platform that allows developers to package applications with their dependencies for easy deployment and scalability.
• Docker enables developers to create lightweight, isolated containers that can run on any operating system.

• It simplifies the deployment process by ensuring that the application and its dependencies are bundled together, eliminating compatibility issues.

• Docker allows for easy sc...read more
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Q4. What is the difference between 'git pull' and 'git fetch'?
Ans. 
Git pull combines git fetch and git merge, while git fetch only downloads new data from a remote repository.
• Git pull is used to update the local branch with the latest changes from the remote repository.

• Git fetch only downloads new data from the remote repository, but does not integrate it into the local branch.

• Git pull is a combination of git fetch and git merge commands.

• Git fetch is useful to see what changes have be...read more
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Q1. Core Java questions and get max o(n) from stack.
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Round duration - 90 minutes
Round difficulty - Medium

It was in the evening, at around 3 - 4 PM. There were 3 coding questions. One easy, two moderate ones. The platform had autocomplete feature too.

Q1. 
Problem Statement: Parity Move
You have an array of integers, and your task is to modify the array by moving all even numbers to the beginning while placing all odd numbers at the end. The order within ev...read more
Ans. 
Move all even numbers to the beginning and odd numbers to the end of an array.
• Iterate through the array and swap even numbers to the front and odd numbers to the back.

• Use two pointers, one starting from the beginning and one from the end, to achieve the desired arrangement.

• Return the modified array with even numbers at the start and odd numbers at the end.
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Q2. 
Anagram Pairs Verification Problem
Your task is to determine if two given strings are anagrams of each other. Two strings are considered anagrams if you can rearrange the letters of one string to form the...read more
Ans. 
Determine if two strings are anagrams of each other by checking if they have the same characters in different order.
• Create a character frequency map for both strings and compare them.

• Sort both strings and compare if they are equal.

• Use a hash table to store character counts and check if they are the same for both strings.
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Q3. 
LCA in a Binary Search Tree
You are given a binary search tree (BST) containing N nodes. Additionally, you have references to two nodes, P and Q, within this BST.
Your task is to determine the Lowest Com...read more
Ans. 
Find the Lowest Common Ancestor (LCA) of two nodes in a Binary Search Tree (BST).
• Traverse the BST from the root node to find the LCA of the given nodes.

• Compare the values of the nodes with the values of P and Q to determine the LCA.

• If the values of P and Q are on opposite sides of the current node, then the current node is the LCA.
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Round duration - 50 Minutes
Round difficulty - Medium

They asked 2 coding questions and 2 sql queries in this round

Q1. 
Find the Longest Palindromic Substring
Given a string ‘S’ composed of lowercase English letters, your task is to identify the longest palindromic substring within ‘S’.
If there are multiple longest palin...read more
Ans. 
Find the longest palindromic substring in a given string, returning the rightmost one if multiple exist.
• Iterate through each character in the string and expand around it to find palindromes

• Keep track of the longest palindrome found and its starting index

• Return the substring starting from the index of the longest palindrome found
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Q2. 
Trapping Rain Water Problem Statement
You are given a long type array/list ARR of size N, representing an elevation map. The value ARR[i] denotes the elevation of the ith bar. Your task is to determine th...read more
Ans. 
Calculate the total amount of rainwater that can be trapped between given elevations in an array.
• Iterate through the array and calculate the maximum height on the left and right of each bar.

• Calculate the amount of water that can be trapped at each bar by taking the minimum of the maximum heights on the left and right.

• Sum up the trapped water at each bar to get the total trapped water for the entire array.
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Q3. What is a nested SQL query?
Ans. 
A nested SQL query is a query within another query, used to retrieve data from multiple tables in a single query.
• Nested queries are enclosed within parentheses and can be used in SELECT, INSERT, UPDATE, or DELETE statements.

• They are commonly used to perform subqueries to filter results based on the output of the inner query.

• Example: SELECT * FROM table1 WHERE column1 IN (SELECT column2 FROM table2 WHERE condition);
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Round duration - 50 Minutes
Round difficulty - Medium

This round was about OS, networking and my projects. What are the different ways to style a React component?
Name a few techniques to optimize React app performance.

Round duration - 30 Minutes
Round difficulty - Easy

It was a fun round, in which they ask about your preferences about programming languages, technologies or your hobbies. If you reach this round, it means that your chances of selection are 99%.

Q1. What was the biggest hurdle you faced while developing a project?
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