National Payments Corporation of India Software Developer Interview Questions and Answers

Round duration - 90 Minutes
Round difficulty - Hard

Timing was 11 am. Platform was quite well.

Q1. 
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 source to destination.
• Use backtracking to explore all possible paths in the maze.

• Keep track of visited cells to avoid revisiting them.

• Explore all possible directions (up, down, left, right) from each cell.

• Add the current direction to the path and recursively explore further.

• When reaching the destination, add the path to the list of valid paths.
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Q2. 
Minimum Cost to Destination
You are given an NxM matrix consisting of '0's and '1's. A '1' signifies that the cell is accessible, whereas a '0' indicates that the cell is blocked. Your task is to compute ...read more
Ans. 
Find the minimum cost to reach a destination in a matrix with blocked cells.
• Use Breadth First Search (BFS) algorithm to explore all possible paths from the starting point to the destination.

• Keep track of the cost incurred at each cell and update it as you move through the matrix.

• Return the minimum cost to reach the destination or -1 if it is unreachable.

• Consider edge cases such as when the starting point is the destina
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Round duration - 90 Minutes
Round difficulty - Easy

This round was conducted on the HackerEarth platform. It had 2 sections and candidates were given a time of 1 hour 30 minutes. 

Programming MCQs — 18 MCQs (each of 2 marks)
Questions were a little tricky. it tested upon one’s programming fundamentals. It had C/C++ output questions, pseudocode questions, Operating systems, and SQL queries.
Coding — 2 ( one contains 75 marks and the other contains 100 marks )

Our scores of the first 2 sections weren’t revealed. My MCQs went really well. I solved 2 coding questions in the coding section. Only 15 students got selected for the interview round, and I was one of them.

Q1. 
Count Ways to Complete Journey in Triangular Pyramid
Given a triangular pyramid with vertices marked as ‘O’, ‘X’, ‘Y’, and ‘Z’, and an integer 'N', you need to calculate the number of ways Bob can start a...read more
Ans. 
Calculate the number of ways to complete a journey in a triangular pyramid starting and ending at a specific vertex after taking a certain number of steps.
• Use dynamic programming to calculate the number of ways to return to the starting vertex after 'N' steps.

• Consider the possible movements from each vertex to adjacent vertices.

• Keep track of the number of ways to reach each vertex after each step.

• Return the total numbe...read more
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Q2. 
Maximum Profit Problem Statement
Mukesh is evaluating the maximum profit from his business over a series of days. Given a list of profits over 'N' days, Mukesh wants to determine the highest profit achiev...read more
Ans. 
The task is to find the maximum profit achievable over any consecutive days within a specified range {‘A’, ‘B’}.
• Iterate through the profit array and calculate the cumulative sum for each possible consecutive days within the range {‘A’, ‘B’}.

• Keep track of the maximum profit obtained during the iteration.

• Return the maximum profit as the final result.
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Round duration - 60 Minutes
Round difficulty - Medium

This round was scheduled for 1 hour and the panel had 1 interviewer. Being a virtual interview, the first challenge that I faced was that the interviewer was not audible. I suggest you not panic in such a situation and use the chatbox feature (or contact HR if need be) to figure out something that works for you and the panel. We later connected over voice call (over the phone) with our videos ON (over a laptop) and continued with the interview.

The interview was very calm and helpful. I was able to solve all questions and I explained different approaches to solve the questions. Once he was convinced of my solution, he asked me to write the code on my own IDE.

Q1. 
Running Median Problem
Given a stream of integers, calculate and print the median after each new integer is added to the stream.
Output only the integer part of the median.
Example:
Input:
N = 5  
Stre...read more
Ans. 
Calculate and print the median after each new integer is added to the stream.
• Use a min heap to store the larger half of the numbers and a max heap to store the smaller half

• Keep the sizes of the two heaps balanced to efficiently calculate the median

• If the total number of elements is odd, the median will be the top element of the max heap

• If the total number of elements is even, the median will be the average of the top e
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Q2. 
Boundary Traversal of a Binary Tree
Given a binary tree of integers, your task is to return the boundary nodes of the tree in Anti-Clockwise direction starting from the root node.
Input:
The first line ...read more
Ans. 
Return the boundary nodes of a binary tree in Anti-Clockwise direction starting from the root node.
• Traverse the left boundary nodes in a top-down manner

• Traverse the leaf nodes from left to right

• Traverse the right boundary nodes in a bottom-up manner

• Handle cases where duplicates occur in the boundary nodes

• Implement the function without printing as printing is already managed
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Q3. 
Count Pairs with Given Sum
Given an integer array/list arr and an integer 'Sum', determine the total number of unique pairs in the array whose elements sum up to the given 'Sum'.
Input:
The first line c...read more
Ans. 
Count the total number of unique pairs in an array whose elements sum up to a given value.
• Use a hashmap to store the frequency of each element in the array.

• Iterate through the array and for each element, check if (Sum - current element) exists in the hashmap.

• Increment the count of pairs if the complement exists in the hashmap.
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Round duration - 90 Minutes
Round difficulty - Medium

This was a technical + HR round. First, he asked me to introduce myself. This round was also based on your knowledge of DSA. I was asked 2 coding questions. Then he asked a couple of questions from OS and DBMS which were pretty easy. At last, we ended the interview on a good note. Then he asked me questions about myself.
Why I want to join OYO rooms. 
What are my hobbies?
Goals in the next five years.

Q1. 
Zig-Zag String Problem Statement
Given a string 'STR' of length 'N' and an integer 'M' representing the number of rows in the zig-zag pattern, your task is to return the string formed by concatenating all...read more
Ans. 
Given a string and number of rows, return the concatenated string formed by arranging the input string in a zig-zag pattern over the specified number of rows.
• Iterate through the string and distribute characters in zig-zag pattern over 'M' rows

• Keep track of the direction of movement (up or down) while distributing characters

• Concatenate characters row-wise to get the final zig-zag pattern string
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Q2. 
Ways To Make Coin Change
Given an infinite supply of coins of varying denominations, determine the total number of ways to make change for a specified value using these coins. If it's not possible to make...read more
Ans. 
The task is to find the total number of ways to make change for a specified value using given denominations.
• Use dynamic programming to solve this problem efficiently.

• Create a 2D array to store the number of ways to make change for each value using different denominations.

• Iterate through the denominations and update the array accordingly.

• The final answer will be stored in the last cell of the array.

• Consider edge cases l
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Round duration - 90 Minutes
Round difficulty - Medium

Q1. 
Fruits and Baskets Problem Statement
You are given 'n' fruit trees planted along a road, numbered from 0 to n-1. Each tree bears a fruit type represented by an uppercase English alphabet. A Ninja walking ...read more
Ans. 
The problem is to find the maximum number of fruits the Ninja can put in both baskets after satisfying given conditions.
• The Ninja can start at any tree and end at any tree, but cannot skip a tree.

• He can pick one fruit from each tree until he cannot, i.e., when he has to pick a fruit of the third type.

• The restriction is that each basket can have only one type of fruit.

• We need to find the maximum number of fruits that ca
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Round duration - 30 Minutes
Round difficulty - Medium

Was Shortlisted For this round with in total of 22 students, 7 in my profile.
It was Technical round with 30 mins of time allotted.
The interviewer was friendly, started with basic questions about me followed by project specific and then a puzzle.

Q1. 
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. 
The problem requires sorting an array of 0s, 1s, and 2s in a single scan.
• Use three pointers to keep track of the positions of 0s, 1s, and 2s.

• Initialize the low pointer at the beginning of the array and the high pointer at the end.

• Iterate through the array using a current pointer and swap elements based on their values.

• Move the pointers accordingly until the array is sorted.

• The time complexity of this solution is O(N) a
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Round duration - 20 Minutes
Round difficulty - Hard

The interview was scheduled for 15 mins and 12 students were shortlisted for this round. 5 in my profile.
The interviewer didn't on his video whereas mine was, the interviewer was friendly and maintained a poker voice.
Asked Basic HR questions but crossed questioned several times.

Q1. General discussion on experience
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Q1. Knowledge on SQL and how to write a query
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Q2. Knowledge on DSA and coding problems to solve.
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Q3. Knowledge on APIS (structure, security etc.)
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78 mcq questions and 2 dsa

Coding based round on dsa

Normal MCQ questions on JS

Write a program to use debouncing in frontend

Q1. Behavioural questions
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Q2. Why this company and why you?
Ans. 
I am passionate about the company's innovative projects and believe my skills align well with the team's goals.
• I have been following the company's work closely and am impressed by their commitment to cutting-edge technology.

• I believe my experience in software development, particularly in the areas of machine learning and AI, would be a valuable addition to the team.

• I am excited about the opportunity to work with a tale...read more
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Q1. REST API for User CRUD
Ans. 
Design a RESTful API for CRUD operations on user resources.
• Use HTTP methods like GET, POST, PUT, DELETE for CRUD operations

• Create endpoints like /users for listing all users, /users/{id} for specific user

• Use status codes like 200 for success, 404 for not found, 400 for bad request

• Implement authentication and authorization mechanisms for security

• Include request and response body formats like JSON or XML
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Q2. Two Sum Leetcode problem
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Q3. Basic questions based on the candidate technical skills
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Q1. Basics to Intermediate level of questions based on the skills mentioned in the resume
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Q2. Projects related discussions
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Q1. I was informed to upload the supporting documents. ( They rejected me after this eventhough all my documents are genuine )
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