National Payments Corporation of India L2 Network Engineer Interview Questions and Answers

Round duration - 90 minutes
Round difficulty - Medium

Q1. 
Rotate Matrix Right K Times
You are given a matrix MAT of size 'N' * 'M', where 'N' is the number of rows and 'M' is the number of columns, along with a positive integer 'K'. Your task is to rotate the ma...read more
Ans. 
Rotate a matrix to the right 'K' times by shifting each column to the right 'K' times.
• Iterate 'K' times to perform right rotation on the matrix

• Shift each column to the right by one position in each rotation

• Handle wrapping around the matrix when shifting columns

• Return the matrix elements row-wise after 'K' rotations
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Q2. 
Word Search Problem Statement
Given a two-dimensional grid of size N x M consisting of upper case characters and a string 'WORD', determine how many times the 'WORD' appears in the grid.
The 'WORD' can b...read more
Ans. 
Count how many times a given word appears in a 2D grid by moving in any of the eight possible directions.
• Iterate through each cell in the grid and check if the word can be formed starting from that cell in any of the eight directions.

• Use recursion to explore all possible paths from a starting cell to form the word.

• Keep track of visited cells to avoid revisiting the same cell in the same path.

• Return the count of how man
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Round duration - 75 minutes
Round difficulty - Medium

Interview started with an introduction and walk through the resume for first 5 minutes. After that, interview asked few coding questions.

Q1. 
Problem Statement: Largest Island
You are provided with a non-empty grid consisting of only 0s and 1s. Your task is to determine the maximum area of an island within the given grid.
An island consists of a...read more
Ans. 
Find the maximum area of an island in a grid of 0s and 1s.
• Iterate through the grid and perform depth-first search (DFS) to find connected 1s.

• Keep track of the area of each island found and return the maximum area.

• Consider all four directions (horizontal, vertical, and diagonal) while exploring the island.

• Handle edge cases like grid boundaries and already visited cells during DFS.

• If no island is present, return 0 as the
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Q2. 
Pythagorean Triplet Problem
Determine if there exists a Pythagorean triplet within a given array of integers. A Pythagorean triplet consists of three numbers, x, y, and z, such that x^2 + y^2 = z^2.
Expl...read more
Ans. 
Check if there exists a Pythagorean triplet in a given array of integers.
• Iterate through all possible triplets in the array and check if they form a Pythagorean triplet.

• Use a nested loop to generate all possible combinations of three numbers from the array.

• Check if the sum of squares of two numbers is equal to the square of the third number.
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Q3. 
Top View of Binary Tree Problem Statement
Given a Binary Tree of integers, you are tasked with finding the top view of the binary tree. The top view is the set of nodes visible when the tree is viewed fro...read more
Ans. 
Find the top view of a Binary Tree by returning a list of visible nodes when viewed from the top.
• Traverse the Binary Tree in level order and keep track of the horizontal distance of each node from the root.

• Use a map to store the nodes at each horizontal distance, and only keep the topmost node for each horizontal distance.

• Return the values of the topmost nodes in the map as the top view of the Binary Tree.
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Round duration - 90 minutes
Round difficulty - Medium

This round was focused on DSA along with short discussion on computer science fundamentals. For coding problems, I was asked to code the first problem only. For others, had to discuss the approach only. For computer science fundamentals, discussion on OOPS. Differences between process and threads were discussed.

Q1. 
Fixing a Swapped Binary Search Tree
Given a Binary Search Tree (BST) where two nodes have been swapped by mistake, your task is to restore or fix the BST without changing its structure.
Input:
The first...read more
Ans. 
Restore a Binary Search Tree by fixing two swapped nodes without changing its structure.
• Identify the two nodes that are swapped by mistake in the BST.

• Swap the values of the two identified nodes to restore the BST.

• Perform an in-order traversal of the BST to verify the correct restoration.

• Ensure no extra space other than the recursion stack is used for the solution.
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Q2. 
Implement Stack with Linked List
Your task is to implement a Stack data structure using a Singly Linked List.
Explanation:
Create a class named Stack which supports the following operations, each in O(1...read more
Ans. 
Implement a Stack data structure using a Singly Linked List with operations like getSize, isEmpty, push, pop, and getTop in O(1) time.
• Create a class named Stack with methods for getSize, isEmpty, push, pop, and getTop.

• Use a Singly Linked List to store the elements of the stack.

• Ensure that each operation runs in constant time O(1).

• Handle edge cases like empty stack appropriately.

• Test the implementation with sample queri
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Aptitude auestions were there

In this round 14 mcq and 2 sql queries were given

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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General apti questions and coding

Q1. Sql , rdbms, projects
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Q1. Hr Questions and projects discussion
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Q1. Project related
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Q2. How you solve questions
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Q1. What is treeset and weakhashmap?
Ans. 
TreeSet is a sorted set implementation in Java. WeakHashMap is a hash table-based Map implementation with weak keys.
• TreeSet is implemented using a tree structure and maintains elements in sorted order.

• WeakHashMap is a Map implementation that allows keys to be garbage collected when they are no longer referenced.

• WeakHashMap is useful for caching or memoization where the keys are not always needed and can be garbage coll
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Q2. What is comparable and comparator?
Ans. 
Comparable and Comparator are interfaces used for sorting objects in Java.
• Comparable interface is used to define the natural ordering of objects based on their own class.

• Comparator interface is used to define the ordering of objects based on a separate class.

• Comparable interface has compareTo() method while Comparator interface has compare() method.

• Comparable interface is implemented by the class whose objects need to ...read more
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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.