RapiPay Node JS Developer Interview Questions and Answers

Round duration - 45 minutes
Round difficulty - Medium

I applied thorough LinkedIn and got a call from HR for the interview.
I went to their Noida Office.
First round was mainly focused on Javascript fundamentals.
Interviewer was also friendly.

Round duration - 1 hour
Round difficulty - Medium

Second round was after 15 minutes of the first round. The focus of this round was DS & Algorithms.

Q1. 
Find Subarray with Given Sum
Given an array ARR of N integers and an integer S, determine if there exists a subarray (of positive length) within the given array such that the sum of its elements equals S....read more
Ans. 
Given an array and a target sum, find a subarray that sums up to the target sum.
• Iterate through the array while keeping track of the running sum and the starting index of the subarray.

• Use a hashmap to store the running sum and its corresponding index.

• If the running sum - target sum is found in the hashmap, it means a subarray with the target sum exists.

• Return the starting and ending indices of the subarray or [-1, -1]
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Q2. 
Minimum Number of Platforms Required
You are provided with two arrays, AT and DT, representing the arrival and departure times of all trains arriving at a railway station.
Your task is to determine the m...read more
Ans. 
This question asks to find the minimum number of platforms required at a railway station so that no train needs to wait.
• Sort the arrival and departure times arrays in ascending order.

• Initialize a variable 'platforms' to 1 and 'maxPlatforms' to 1.

• Iterate through the arrival and departure times arrays simultaneously.

• If the current arrival time is less than or equal to the current departure time, increment 'platforms'.

• If ...read more
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Round duration - 30 minutes
Round difficulty - Easy

Q1. What JavaScript questions did he ask you during the managerial round, and can you describe the work culture of his team?
Ans. 
The interviewer asked about JavaScript questions and the work culture of the team during the managerial round.
• JavaScript questions related to closures, prototypes, event handling, and asynchronous programming may have been asked.

• Work culture may involve collaboration, innovation, agile methodologies, and continuous learning.

• Examples of work culture could include regular team meetings, code reviews, hackathons, and ment
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Round duration - 15 minutes
Round difficulty - Easy

DS/ALGO and problem-solving was asked in round one

Round duration - 90 minutes
Round difficulty - Medium

Started with projects discussion and internships and moved forward with coding problems.
It started at around 6:00 PM and lasted for 90 minutes approximately
The interviewer was very cool, he even gave me some tips on improving myself further at the end of the interview.

Q1. 
Longest Substring with At Most K Distinct Characters
Given a string S of length N and an integer K, find the length of the longest substring that contains at most K distinct characters.
Input:
The first...read more
Ans. 
Find the length of the longest substring with at most K distinct characters in a given string.
• Use a sliding window approach to keep track of the characters and their counts within the window.

• Maintain a hashmap to store the characters and their frequencies.

• Update the window size and characters count as you iterate through the string.

• Return the maximum window size encountered for each test case.
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Q2. 
Maximum Frequency Number Problem Statement
Given an array of integers with numbers in random order, write a program to find and return the number which appears the most frequently in the array.
If multip...read more
Ans. 
Find the number with the maximum frequency in an array of integers.
• Iterate through the array and keep track of the frequency of each number using a hashmap.

• Find the number with the maximum frequency and return it.

• If multiple elements have the same maximum frequency, return the one that appears first.
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Q3. 
Ninja and Bombs Problem Statement
Ninja wants to travel from his house to his best friend's house. The locations of the houses are on a 2D coordinate plane, where Ninja's house is located at the origin (0...read more
Ans. 
Determine if Ninja can reach his friend's house with even x-coordinate without using modulus operator.
• Check if the x-coordinate is even or odd by using bitwise AND operation with 1.

• Return 1 if x-coordinate is even, else return 0.

• Handle multiple test cases by iterating through each input.
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Round duration - 60 minutes
Round difficulty - Easy

I was asked a coding question then, a system design question and some basic operating systems and oops questions

Q1. 
Find Duplicates in an Array
Given an array ARR of size 'N', where each integer is in the range from 0 to N - 1, identify all elements that appear more than once.
Return the duplicate elements in any orde...read more
Ans. 
Find duplicates in an array of integers within a specified range.
• Iterate through the array and keep track of the count of each element using a hashmap.

• Return elements with count greater than 1 as duplicates.

• Time complexity can be optimized to O(N) using a set to store seen elements.
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Q2. Can you design a Google Search Engine?
Ans. 
Designing a Google Search Engine involves creating a web crawler, indexing system, and ranking algorithm.
• Develop a web crawler to discover and retrieve web pages.

• Implement an indexing system to store and organize the content of web pages.

• Design a ranking algorithm to determine the relevance of search results.

• Include features like autocomplete, spell check, and personalized search results.

• Optimize for speed and scalabil...read more
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Round duration - 120 Minutes
Round difficulty - Medium

The first round was an assessment round comprised of MCQ questions of DSA, RDBMS, MySQL questions and 2 coding questions to be written in java only

Q1. 
Shortest Path in a Binary Matrix Problem Statement
Given a binary matrix of size N * M where each element is either 0 or 1, find the shortest path from a source cell to a destination cell, consisting only...read more
Ans. 
Find the shortest path in a binary matrix from a source cell to a destination cell consisting only of 1s.
• Use Breadth First Search (BFS) to explore all possible paths from the source cell to the destination cell.

• Keep track of visited cells to avoid revisiting them.

• Update the path length as you traverse through the matrix.

• Return the shortest path length found or -1 if no valid path exists.
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Q2. 
Kth Smallest Element Problem Statement
You are provided with an array of integers ARR of size N and an integer K. Your task is to find and return the K-th smallest value present in the array. All elements...read more
Ans. 
Find the K-th smallest element in an array of distinct integers.
• Sort the array and return the element at index K-1.

• Use a min-heap to find the K-th smallest element efficiently.

• Implement quickselect algorithm for optimal performance.
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Round duration - 60 Minutes
Round difficulty - Medium

The basic data structure round duration 1 hour, in this Interviewer, was very friendly and asked some casual questions. After that, he asked me to code.

Q1. 
Maximum Subarray Sum Problem Statement
Given an array of integers, determine the maximum possible sum of any contiguous subarray within the array.
Example:
Input:
array = [34, -50, 42, 14, -5, 86]
Out...read more
Ans. 
Find the maximum sum of any contiguous subarray within an array of integers.
• Iterate through the array and keep track of the maximum sum of subarrays encountered so far.

• At each index, decide whether to include the current element in the subarray or start a new subarray.

• Update the maximum sum if a new maximum is found.

• Example: For array [34, -50, 42, 14, -5, 86], the maximum sum is 137.

• Example: For array [-5, -1, -8, -9]
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Round duration - 60 Minutes
Round difficulty - Hard

Advance data structure round duration 1 hour, in this Interviewer asked some basic questions on oops, puzzles and asked me to code them later.

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 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 as the last node encountered during the reversal process.
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Q2. 
Trapping Rain Water
You are provided with an array ARR of integers representing an elevation map, where ARR[i] denotes the elevation of the ith bar. Determine the maximum amount of rainwater that can be t...read more
Ans. 
Given an array representing an elevation map, find the maximum amount of rainwater that can be trapped between the bars.
• Iterate through the array and calculate the maximum height on the left and right of each bar.

• Calculate the trapped water by finding the minimum of the maximum heights on the left and right minus the current bar height.

• Sum up the trapped water for all bars to get the total trapped rainwater.

• Example: Fo...read more
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Round duration - 30 Minutes
Round difficulty - Medium

Vice President interview round duration 30mins, in this round VP’s of different domains taking interview to the selected candidates.

Q1. 
Buy and Sell Stock Problem Statement
Imagine you are Harshad Mehta's friend, and you have been given the stock prices of a particular company for the next 'N' days. You can perform up to two buy-and-sell ...read more
Ans. 
The task is to determine the maximum profit that can be achieved by performing up to two buy-and-sell transactions on a given set of stock prices.
• Iterate through the array of stock prices to find the maximum profit that can be achieved by buying and selling stocks.

• Keep track of the maximum profit that can be obtained by performing two transactions.

• Consider all possible combinations of buying and selling stocks to maxim...read more
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Round duration - 30 Minutes
Round difficulty - Easy

This round lasted for 30mins basic HR questions were asked

Round duration - 90 minutes
Round difficulty - Medium

Only Java allowed

Q1. 
Sort 0 and 1 Problem Statement
Given an integer array ARR of size N containing only integers 0 and 1, implement a function to sort this array. The solution should scan the array only once without using an...read more
Ans. 
Sort an array of 0s and 1s in linear time without using additional arrays.
• Iterate through the array and maintain two pointers, one for 0s and one for 1s.

• Swap elements at the two pointers based on the current element being 0 or 1.

• Continue this process until the entire array is sorted in place.
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Round duration - 60 minutes
Round difficulty - Easy

Basic intro and coding questions

Q1. 
Valid Perfect Square Check
An integer N is provided, and the task is to determine if N is a perfect square. A perfect square refers to an integer which can be expressed as the square of another integer.
...read more
Ans. 
Implement a function to check if a given integer is a perfect square.
• Create a function that takes an integer as input and returns true if it is a perfect square, false otherwise.

• Iterate through possible square roots of the input integer and check if the square of the root equals the input.

• Return true if a perfect square is found, false otherwise.
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Q2. 
Merge Sort Problem Statement
Given a sequence of numbers 'ARR', your task is to return a sorted sequence of 'ARR' in non-descending order using the Merge Sort algorithm.
Example:
Input:
ARR = [5, 3, 8,...read more
Ans. 
Implement Merge Sort algorithm to sort a given sequence of numbers in non-descending order.
• Merge Sort is a divide-and-conquer algorithm that splits the array into two halves, recursively sorts each half, and then merges the sorted halves back together.

• Time complexity of Merge Sort is O(n log n) in the worst case scenario.

• It is a stable sorting algorithm, meaning that the relative order of equal elements is preserved.

• Ex...read more
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Round duration - 60 minutes
Round difficulty - Medium

More difficult than the previous round

Q1. 
Bottom View of Binary Tree Problem Statement
Given a binary tree, the task is to print its bottom view from left to right. Assume the left and the right child nodes make a 45-degree angle with their paren...read more
Ans. 
The task is to print the bottom view of a binary tree from left to right.
• Traverse the binary tree in level order and keep track of the horizontal distance of each node from the root.

• Store the nodes at each horizontal distance in a map, updating it as you traverse the tree.

• After traversal, extract the bottom-most nodes at each horizontal distance to get the bottom view sequence.
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Round duration - 70 minutes
Round difficulty - Medium

There were no DSA questions. My interviews were based on android app development. The interviewer presented scenarios and asked how will you solve them. No particular correct answer was expected just the best approach as per me.

Q1. How would you implement multiple RecyclerViews on a magnified screen in an Android application?
Ans. 
Implement multiple RecyclerViews on a magnified screen in an Android app by adjusting item sizes and spacing.
• Adjust item sizes and spacing based on screen magnification level

• Use nested RecyclerViews or custom layouts to display multiple lists

• Implement custom item decorators to manage spacing between RecyclerViews

• Consider using a GridLayoutManager with custom span sizes for each RecyclerView
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Q2. How would you implement various activities related to cart functionality in an e-commerce application?
Ans. 
Implementing cart functionality in an e-commerce application involves managing user interactions, updating quantities, handling discounts, and processing orders.
• Create a data structure to store cart items, quantities, and prices.

• Implement add to cart, remove from cart, and update quantity functionalities.

• Handle discounts, promotions, and coupon codes.

• Calculate total price, including taxes and shipping costs.

• Implement c...read more
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Round duration - 30 minutes
Round difficulty - Easy

HR asked questions about why Mobikwik, what's your goal, how are you a good fit, etc.