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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It will be a basic maths questions.

As a general topic of trend in world.

To be known for programming knowledge about us.

Q1. Programming oridanited
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Q2. Skill knowledge questions
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Q1. Tell me about your self.
Ans. 
I am a passionate Full Stack Developer with experience in building web applications using various technologies.
• Experienced in front-end technologies like HTML, CSS, JavaScript, and frameworks like React and Angular

• Proficient in back-end technologies like Node.js, Express, and databases like MongoDB and SQL

• Familiar with version control systems like Git and deployment tools like Heroku
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Q2. Family background .
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Q1. Sal queries simeple data structure question finding largest number in am array.
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Q2. Solid principal
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Round duration - 120 Minutes
Round difficulty - Medium

This was a coding round conducted from 12 PM to 2 PM and it was not proctored but we could not switch the tabs. There were 2 coding questions each of 100 marks. The MCQ had HTML,CSS, JS, SQL, Coding and aptitutude questions.

Q1. 
N Queens Problem
Given an integer N, find all possible placements of N queens on an N x N chessboard such that no two queens threaten each other.
Explanation:
A queen can attack another queen if they ar...read more
Ans. 
The N Queens Problem involves finding all possible placements of N queens on an N x N chessboard where no two queens threaten each other.
• Use backtracking algorithm to explore all possible configurations.

• Keep track of rows, columns, and diagonals to ensure queens do not threaten each other.

• Generate valid configurations recursively and backtrack when a solution is not possible.
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Q2. 
Rearrange String Problem Statement
Given a string ‘S’, your task is to rearrange its characters so that no two adjacent characters are the same. If it's possible, return any such arrangement, otherwise re...read more
Ans. 
Given a string, rearrange its characters so that no two adjacent characters are the same. Return 'Yes' if possible, 'No' otherwise.
• Iterate through the string and count the frequency of each character

• Use a priority queue to rearrange characters based on frequency

• Check if the rearranged string has no two adjacent characters the same

• Return 'Yes' if possible, 'No' otherwise
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Round duration - 60 minutes
Round difficulty - Easy

There were two interviewers. They started by asking me to introduce myself and asked me to explain any one of my projects in my resume and after that, they asked me about the ML algorithms used in my project and about the difficulties faced. What is NaN property in JavaScript? This took around 10 minutes. They also asked 2 coding questions.
It was conducted at 10 AM on CodePair and MS Teams. Interviewers were friendly.

Q1. 
Group Anagrams Together
Given an array/list of strings STR_LIST, group the anagrams together and return each group as a list of strings. Each group must contain strings that are anagrams of each other.
E...read more
Ans. 
Group anagrams in a list of strings together and return each group as a list of strings.
• Iterate through the list of strings and sort each string alphabetically to create a key for grouping.

• Use a hashmap to store the sorted string as key and the original string as value.

• Return the values of the hashmap as the grouped anagrams.
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Q2. 
Friends Pairing Problem
The task is to determine the total number of ways to pair up 'N' friends or leave some of them single, following these rules:
1. Each friend can either pair with one other friend ...read more
Ans. 
The task is to determine the total number of ways to pair up 'N' friends or leave some of them single.
• Use dynamic programming to solve the problem efficiently.

• Consider the base cases when N is 1, 2, and 3 to derive the general formula.

• The result should be computed modulo 10^9 + 7 to handle large outputs.
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Round duration - 60 Minutes
Round difficulty - Medium

There were 2 questions based on data structures, the round started from 1.15 PM .Some SQL questions like What is a Subquery? What are its types? What are UNION, MINUS and INTERSECT commands?

Q1. 
Vertical Order Traversal Problem Statement
You are given a binary tree, and the task is to perform a vertical order traversal of the values of the nodes in the tree.
For a node at position ('X', 'Y'), th...read more
Ans. 
Perform vertical order traversal of a binary tree based on decreasing 'Y' coordinates.
• Traverse the binary tree level by level and maintain the position of each node

• Use a map to store nodes at each position and sort them based on 'Y' coordinates

• Print the nodes in sorted order for each position to get the vertical order traversal
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Q2. 
Divide Two Integers Problem Statement
You are given two integers dividend and divisor. Your task is to divide the integers without using multiplication, division, and modular operators. Return the quotien...read more
Ans. 
Divide two integers without using multiplication, division, and modular operators, returning the floored value of the quotient.
• Implement division using bit manipulation and subtraction

• Handle edge cases like negative numbers and overflow

• Return the floored value of the quotient
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Round duration - 30 Minutes
Round difficulty - Easy

The round was at 7.30 PM and I was asked to introduce myself and we had basic talk on where I live and my interests. I asked about the work culture and about the role at the end.

Q1. You are presented with a puzzle where there are n balloons, and your task is to burst the maximum number of balloons using an arrow. How would you approach solving this puzzle?
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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 - 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 - 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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