Zellis Interview Questions, Process, and Tips

Round duration - 60 minutes
Round difficulty - Medium

This was a 60 minute technical round where the interviewer asked programming based questions and questions on DBMS concepts.

Q1. 
Maximum of All Subarrays of Size k
Given an array of 'N' non-negative integers and an integer 'K', your task is to find the maximum elements for each subarray of size 'K'.
Input:
The first line contains...read more
Ans. 
Find the maximum elements for each subarray of size 'K' in an array of non-negative integers.
• Iterate through the array and maintain a deque to store the indices of elements in decreasing order.

• Pop elements from the deque if they are out of the current window of size 'K'.

• The front of the deque will always have the index of the maximum element in the current window.
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Q2. Can you explain the ACID properties in the context of database management systems?
Ans. 
ACID properties are a set of properties that guarantee the reliability of transactions in database management systems.
• Atomicity ensures that either all operations in a transaction are completed successfully or none of them are. For example, transferring money from one account to another should either be completed in full or not at all.

• Consistency ensures that the database remains in a consistent state before and after ...read more
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Q3. What is write-ahead logging in DBMS?
Ans. 
Write-ahead logging is a technique used in DBMS to ensure that changes are recorded in the log before they are applied to the database.
• Write-ahead logging ensures that changes are first written to the log file before being applied to the database to maintain data integrity.

• It helps in recovering the database in case of a system crash or failure by replaying the log entries to bring the database back to a consistent sta...read more
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Q4. What are the deadlock avoidance schemes?
Ans. 
Deadlock avoidance schemes are strategies used to prevent deadlocks in a system.
• Banker's algorithm: Ensures that the system will never enter an unsafe state by keeping track of available resources and only granting a request if it does not lead to a deadlock.

• Wait-die and Wound-wait: Two deadlock prevention schemes used in transaction processing systems to avoid deadlocks by allowing transactions to wait or abort based ...read more
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Q5. What is a clustered index?
Ans. 
A clustered index is a type of index that sorts and stores the data rows in the table based on their key values.
• Defines the order in which data is physically stored in a table

• Only one clustered index per table

• Helps in improving the performance of queries that involve range searches or sorting

• Example: Clustered index on a table's primary key
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Round duration - 60 minutes
Round difficulty - Easy

This was a 60 minute technical round where the interviewer asked data structure based questions, questions on OOPS and OS concepts.

Q1. What is a virtual function in C++?
Ans. 
A virtual function in C++ is a function that is declared within a base class and is redefined by a derived class.
• Virtual functions allow a function to be overridden in a derived class.

• They are used in polymorphism to achieve runtime binding.

• The base class function must be declared as virtual for dynamic binding to occur.

• Example: virtual void display() = 0; // pure virtual function
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Q2. Can you explain the malloc() and free() operations in the context of memory management in C?
Ans. 
malloc() is used to dynamically allocate memory in C, while free() is used to release allocated memory.
• malloc() allocates a block of memory of specified size and returns a pointer to the beginning of the block.

• free() deallocates the memory previously allocated by malloc() or calloc().

• Example: int *ptr = (int*)malloc(5 * sizeof(int)); // Allocates memory for 5 integers

• Example: free(ptr); // Deallocates the memory alloca
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Q3. What is structure padding?
Ans. 
Structure padding is the concept of adding empty bytes to a structure to align its data members on memory boundaries.
• Structure padding is done to optimize memory access and improve performance.

• Padding is necessary because most processors require data to be aligned on specific memory boundaries for efficient access.

• For example, if a structure contains a char followed by an int, padding may be added after the char to ali
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Round duration - 30 minutes
Round difficulty - Easy

HR based round that lasted for 30 minutes. The interviewer asked question to know more about me.

Round duration - 90 minutes
Round difficulty - Easy

Online test had 6 parts-psychometric test, aptitude, logical, English, computer skills and 2 coding questions. Time given to us was 90 minutes. Paper was quite lengthy and of average difficulty level. I was able to complete all the sections, but only one coding question.

Q1. 
Reverse the String Problem Statement
You are given a string STR which contains alphabets, numbers, and special characters. Your task is to reverse the string.
Example:
Input:
STR = "abcde"
Output:
"e...read more
Ans. 
Reverse a given string containing alphabets, numbers, and special characters.
• Iterate through the string from the end to the beginning and append each character to a new string.

• Use built-in functions like reverse() or StringBuilder in languages like Python or Java for efficient reversal.

• Handle special characters and numbers while reversing the string.

• Ensure to consider the constraints provided in the problem statement.

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

Firstly the interviewer asked me to introduce myself after he introduced himself. Since i went there as experienced guy he asked me about my workings in the current company. After that,he asked some programming questions, tested my concepts of DBMS and OOPS, and some puzzles.

Q1. 
BFS Traversal in a Graph
Given an undirected and disconnected graph G(V, E) where V vertices are numbered from 0 to V-1, and E represents edges, your task is to output the BFS traversal starting from the ...read more
Ans. 
BFS traversal in a disconnected graph starting from vertex 0.
• Implement BFS algorithm to traverse the graph starting from vertex 0.

• Explore neighbor nodes first before moving to the next level neighbors.

• Consider the bidirectional nature of edges in an undirected graph.

• Output the BFS traversal sequence for each test case in a separate line.
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Q2. 
Prime Numbers Identification
Given a positive integer N, your task is to identify all prime numbers less than or equal to N.
Explanation:
A prime number is a natural number greater than 1 that has no po...read more
Ans. 
Identify all prime numbers less than or equal to a given positive integer N.
• Iterate from 2 to N and check if each number is prime

• Use the Sieve of Eratosthenes algorithm for efficient prime number identification

• Optimize by only checking up to the square root of N for divisors
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Q3. What is BCNF (Boyce-Codd Normal Form) in database management systems?
Ans. 
BCNF is a normal form in database management systems that ensures all determinants are candidate keys.
• BCNF stands for Boyce-Codd Normal Form.

• It is a stricter version of 3NF (Third Normal Form).

• In BCNF, every determinant must be a candidate key.

• It helps in reducing redundancy and anomalies in the database.

• Example: If a table has columns A, B, and C, and A determines B and B determines C, then it is not in BCNF unless A
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Q4. What is the difference between C and C++?
Ans. 
C is a procedural programming language while C++ is an object-oriented programming language with features like classes and inheritance.
• C is a procedural programming language, while C++ is a multi-paradigm language with support for object-oriented programming.

• C does not support classes and objects, while C++ does.

• C uses structures for data organization, while C++ uses classes.

• C does not have features like inheritance an...read more
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Q5. How can you make 3 cuts to divide a round cake into 8 equal pieces?
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Q6. How can you calculate 45 minutes using only 2 candles?
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Round duration - 60 minutes
Round difficulty - Easy

Again 2nd round started with an introduction from both sides. Then he started asking questions from resume itself. Working in the current company and all the projects that i have done. Few simple puzzles, OOPs concepts (with proper explanation and coding) and some database related questions(questions were easy you just need to brush up the basics). Some keywords related questions from C,C++,Java(usual questions like static ,final, abstract etc.). That was the 2nd round. Then I was called for the 3rd Round. Before 3rd round they also served tasty lunch.

Q1. 
Right View of Binary Tree
Given a binary tree of integers, your task is to output the right view of the tree.
The right view of a binary tree includes the nodes that are visible when the tree is observed...read more
Ans. 
The task is to output the right view of a binary tree, which includes the nodes visible when observed from the right.
• Traverse the tree level by level and keep track of the rightmost node at each level.

• Use a queue for level order traversal and a map to store the rightmost nodes.

• Print the values of the rightmost nodes stored in the map as the right view of the tree.
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Q2. You have 3 bulbs in one room and 3 switches in another room. The challenge is to determine which switch controls which bulb, with the constraint that you can only enter the bulb room once.
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Round duration - 45 minutes
Round difficulty - Easy

After that he asked me what I knew about SAP and there products(Please do read all about SAP and there products-not all but at least some famous products like ERP). Then he asked me one puzzle.

Q1. You have 2 eggs and a building with 100 floors. What is the minimum number of attempts needed to find the highest floor from which an egg can be dropped without breaking?
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Round duration - 45 minutes
Round difficulty - Easy

The round started with our Introduction to each other. After that interviewer asked me whether I do online shopping or not. I said yes then he asked me to design the online shopping portal using ER-Diagram . Then he asked me to create all the tables and populate it with data. Later on he asked me to normalize it. After all of this he asked me some simple puzzles and current salary and notice period. That was the 4th round.
After that I was asked to attend the final round and before 5th round they served snacks and tea to all of us.

Q1. Can you design an ER diagram for an online shopping portal?
Ans. 
Yes, I can design an ER diagram for an online shopping portal.
• Entities: User, Product, Order, Payment, Cart

• Relationships: User places Order, Order contains Product, Payment for Order, User has Cart

• Attributes: User (id, name, email), Product (id, name, price), Order (id, date), Payment (id, amount)
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Round duration - 60 minutes
Round difficulty - Easy

The test had a time limit. Every 10 minutes you had to do at least 4 questions. It was quite fast paced. The questions were from basic coding, aptitude and debugging.
Tips: Learn to be fast at coding. Practice a lot of aptitude questions. Have a decent knowledge of basic coding.

Q1. 
Reverse Linked List Problem Statement
Given a Singly Linked List of integers, your task is to reverse the Linked List by altering the links between the nodes.
Input:
The first line of input is an intege...read more
Ans. 
Reverse a singly linked list by altering the links between nodes.
• Iterate through the linked list and reverse the links between nodes

• Use three pointers to keep track of current, previous, and next nodes

• Update the next pointer of each node to point to the previous node
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Q2. 
Longest Substring Without Repeating Characters Problem Statement
Given a string S of length L, determine the length of the longest substring that contains no repeating characters.
Example:
Input:
"abac...read more
Ans. 
Find the length of the longest substring without repeating characters in a given string.
• Use a sliding window approach to keep track of the longest substring without repeating characters.

• Use a hashmap to store the index of each character as it appears in the string.

• Update the start index of the window when a repeating character is found.

• Calculate the maximum length of the substring as the window slides through the strin
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Round duration - 60 minutes
Round difficulty - Easy

The interviewer started off by asking basic sorting questions. Followed by data structures and algorithms. And DBMS related questions in the end.
Tips: Have a good presence of mind. Understand the question asked properly. Be confident and keep discussing. Don't get nervous and solve the questions incorrectly. Have good grip over topics like sorting, DS, Algorithms and DBMS.

Q1. 
LCA of Binary Tree Problem Statement
You are given a binary tree consisting of distinct integers and two nodes, X and Y. Your task is to find and return the Lowest Common Ancestor (LCA) of these two nodes...read more
Ans. 
Find the Lowest Common Ancestor (LCA) of two nodes in a binary tree.
• Traverse the binary tree to find the paths from the root to nodes X and Y.

• Compare the paths to find the last common node, which is the LCA.

• Handle cases where one node is an ancestor of the other.

• Consider edge cases like when X or Y is the root node.

• Implement a recursive or iterative solution to find the LCA efficiently.
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Q2. 
Next Permutation Problem Statement
You are given a permutation of 'N' integers. A sequence of 'N' integers is considered a permutation if it includes all integers from 1 to 'N' exactly once. Your task is ...read more
Ans. 
The task is to rearrange a given permutation of 'N' integers to form the lexicographically next greater permutation.
• Iterate from right to left to find the first element that is smaller than the element to its right.

• Swap this element with the smallest element to its right that is greater than it.

• Reverse the elements to the right of the swapped element to get the lexicographically next greater permutation.
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Round duration - 30 minutes
Round difficulty - Easy

The round was based around my over all personality. They checked how would I be an asset to their company. They analyzed my core values and capabilities of working in a team.
Tips: Show that you are willing to work in a team. Be confident and polite. Express your feelings and passion towards your job and the company. Explain your college extra curricular activities well.

Round duration - 60 minutes
Round difficulty - Easy

This was a technical interview round which lasted for 60 minutes. Questions based on DSA, OS and DBMS were discussed.

Q1. 
Factorial of a Number Problem Statement
You are provided with an integer 'N'. Your task is to calculate and print the factorial of 'N'. The factorial of a number 'N', denoted as N!, is the product of all ...read more
Ans. 
Calculate and print the factorial of a given integer 'N'.
• Iterate from 1 to N and multiply each number to calculate factorial

• Handle edge cases like N=0 or N=1 separately

• Use recursion to calculate factorial efficiently
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Q2. 
Covid Vaccination Distribution Problem
As the Government ramps up vaccination drives to combat the second wave of Covid-19, you are tasked with helping plan an effective vaccination schedule. Your goal is...read more
Ans. 
Maximize the number of vaccines administered on a specific day while adhering to certain rules.
• Given n days, maxVaccines available, and a specific dayNumber, distribute vaccines to maximize on dayNumber

• Administer positive number of vaccines each day with a difference of 1 between consecutive days

• Ensure sum of vaccines distributed does not exceed maxVaccines

• Output the maximum number of vaccines administered on dayNumber
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Q3. What is a semaphore?
Ans. 
A semaphore is a synchronization construct used to control access to a shared resource by multiple processes or threads.
• Semaphores can have an integer value representing the number of available resources.

• They can be used to implement mutual exclusion and synchronization between processes.

• Examples include binary semaphores (mutexes) and counting semaphores.

• Operations on semaphores include wait (P) and signal (V).
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Q4. What is the difference between RDBMS and DBMS?
Ans. 
RDBMS is a type of DBMS that manages data in a structured format using tables with relationships.
• RDBMS enforces referential integrity through foreign keys, while DBMS does not.

• RDBMS supports ACID properties (Atomicity, Consistency, Isolation, Durability), while DBMS may not.

• RDBMS allows for normalization of data to reduce redundancy, while DBMS does not have this feature.

• Examples of RDBMS include MySQL, Oracle, SQL Ser...read more
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Round duration - 60 minutes
Round difficulty - Easy

A 60 minute technical round to test programming concepts. Questions on DBMS, OOPS, OS were also discussed.

Q1. 
Bubble Sort Problem Statement
Sort the given unsorted array consisting of N non-negative integers in non-decreasing order using the Bubble Sort algorithm.
Input:
The first line contains an integer 'T' r...read more
Ans. 
Bubble Sort algorithm is used to sort an array of non-negative integers in non-decreasing order.
• Iterate through the array and compare adjacent elements, swapping them if they are in the wrong order.

• Repeat this process until the array is sorted.

• Time complexity of Bubble Sort is O(n^2) in worst case.

• Space complexity of Bubble Sort is O(1) as it is an in-place sorting algorithm.
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Q2. 
Merge Sort Problem Statement
You are 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.
Explanation:
The Merge Sort...read more
Ans. 
Implement Merge Sort algorithm to sort a sequence of numbers in non-descending order.
• Divide the input array into two halves recursively until each array has only one element.

• Merge the sorted halves to produce a completely sorted array.

• Time complexity of Merge Sort is O(n log n).

• Example: Input: [3, 1, 4, 1, 5], Output: [1, 1, 3, 4, 5]
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Q3. What is normalization in the context of database management systems?
Ans. 
Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity.
• Normalization involves breaking down a database into smaller, more manageable tables.

• It helps in reducing data redundancy by storing data in a structured way.

• There are different normal forms such as 1NF, 2NF, 3NF, BCNF, etc., each with specific rules to follow.

• Normalization ensures data integrity and reduces th...read more
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Round duration - 40 minutes
Round difficulty - Easy

This was a HR round. The interviewer asked me a number of questions about myself and gave a puzzle as well to solve.

Round duration - 100 minutes
Round difficulty - Easy

Sections in test :
1 Psychometric Test
2. Analytical Aptitude
3 Logical Reasoning
4 Two coding Questions
5.Pattern Recognition
6.Essay writing

Tips :

1. Do the coding Question first ,they are mot important ,if your code doesn't run you are disqualified.
2. Practice on leetcode. 
3. Sectional Cutoff

Q1. 
Level Order Traversal Problem Statement
Given a binary tree of integers, return the level order traversal of the binary tree.
Input:
The first line contains an integer 'T', representing the number of te...read more
Ans. 
The task is to implement a function that returns the level order traversal of a binary tree given in level order.
• Create a queue to store nodes for level order traversal

• Start with the root node and enqueue it

• While the queue is not empty, dequeue a node, print its value, and enqueue its children

• Repeat until all nodes are traversed
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Round duration - 60 minutes
Round difficulty - Medium

This was a technical round where the interviewer asked me questions on data structures, database management system, SQL queries, cloud computing concepts and puzzles. We also had a discussion on our projects.

Q1. 
Floyd Warshall Algorithm Problem
You are given a directed weighted graph with 'N' vertices, labeled from 1 to 'N', and 'M' edges. Each edge connects two nodes 'u' and 'v' with a weight 'w', representing t...read more
Ans. 
The Floyd Warshall algorithm is used to find the shortest paths between all pairs of vertices in a graph, including graphs with negative edge weights.
• The algorithm works by considering all pairs of vertices and all intermediate vertices to find the shortest path.

• It can handle graphs with negative edge weights, but not negative weight cycles.

• The time complexity of the algorithm is O(N^3), where N is the number of vertic...read more
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Q2. What would be the database design for an ATM system?
Ans. 
The database design for an ATM system should include tables for users, accounts, transactions, and ATM machines.
• Create a table for users with fields like user_id, name, pin, etc.

• Create a table for accounts with fields like account_id, user_id, balance, etc.

• Create a table for transactions with fields like transaction_id, account_id, amount, date, etc.

• Create a table for ATM machines with fields like atm_id, location, sta
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Q3. What is the difference between public and private cloud?
Ans. 
Public cloud is shared infrastructure available to anyone, while private cloud is dedicated infrastructure for a single organization.
• Public cloud is accessible to multiple organizations or users, while private cloud is exclusive to a single organization.

• Public cloud services are provided over the internet, while private cloud services can be hosted on-premises or in a dedicated data center.

• Public cloud offers cost-effe...read more
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Round duration - 60 minutes
Round difficulty - Easy

Technical Interview round that lasted for 60 minutes. Questions on data structures, DBMS, OS and puzzles were discussed.

Q1. 
Reverse Linked List Problem Statement
Given a Singly Linked List of integers, your task is to reverse the Linked List by altering the links between the nodes.
Input:
The first line of input is an intege...read more
Ans. 
Reverse a singly linked list by altering the links between nodes.
• Iterate through the linked list and reverse the links between nodes

• Use three pointers to keep track of current, previous, and next nodes

• Update the links between nodes to reverse the list

• Return the head of the reversed linked list
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Q2. What is the difference between a primary key and a unique key in a database management system?
Ans. 
Primary key uniquely identifies each record in a table, while unique key ensures that all values in a column are distinct.
• Primary key does not allow NULL values, while unique key allows one NULL value.

• A table can have only one primary key, but multiple unique keys.

• Primary key is automatically indexed, while unique key may or may not be indexed.

• Example: In a table of students, student ID can be a primary key as it uniqu...read more
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Q3. Write a query to find the nth highest salary in a database.
Ans. 
Query to find the nth highest salary in a database
• Use the ORDER BY clause to sort salaries in descending order

• Use the LIMIT clause to specify the nth highest salary

• Consider handling cases where there may be ties for the nth highest salary
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Q4. What is the difference between AES and DES ciphers?
Ans. 
AES is a more secure and efficient cipher compared to DES.
• AES has a block size of 128 bits, while DES has a block size of 64 bits.

• AES supports key sizes of 128, 192, or 256 bits, while DES supports only 56-bit keys.

• AES is considered more secure and efficient than DES due to its stronger encryption algorithm and larger key sizes.
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Q5. You have a torch and a bridge that can only hold two people at a time. Four people need to cross the bridge at night, and they have only one torch. Each person walks at a different speed. When two people c...read more
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Round duration - 30 minutes
Round difficulty - Easy

The lady was tough and showed her intent in the PPT as well. She asked a number of questions to know more about me.