Envoy Global Interview Questions and Answers for Experienced

Round duration - 90 minutes
Round difficulty - Easy

It was on online objective test consisting of 4 sections: Aptitude, Technical MCQs, Code snippet based MCQs and Coding part.

Q1. 
Valid Parentheses Problem Statement
Given a string 'STR' consisting solely of the characters “{”, “}”, “(”, “)”, “[” and “]”, determine if the parentheses are balanced.
Input:
The first line contains an...read more
Ans. 
The task is to determine if a given string of parentheses is balanced or not.
• Iterate through the characters of the string and use a stack to keep track of opening parentheses.

• When encountering an opening parenthesis, push it onto the stack. When encountering a closing parenthesis, check if it matches the top of the stack.

• If the stack is empty at the end or there are unmatched parentheses, the string is not balanced.

• Exa...read more
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Q2. 
Palindrome Linked List Problem Statement
Determine if a given singly linked list of integers is a palindrome. Return true if it is a palindrome, otherwise return false.
Example:
Input:
1 -> 2 -> ...read more
Ans. 
Check if a given singly linked list of integers is a palindrome.
• Use two pointers to find the middle of the linked list.

• Reverse the second half of the linked list.

• Compare the first half with the reversed second half to determine if it is a palindrome.
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Round duration - 60 minutes
Round difficulty - Easy

This was a technical and managerial round. The interviewer gave me a situation where I am in testing team and I found that customer requirement was drop down list at a place but developer has used bullet selection, and is not ready to change it. How will you manage? I gave some good replies and he was convinced.

Q1. What is a virtual function?
Ans. 
A virtual function is a function in a base class that is declared using the keyword 'virtual' and can be overridden by a function with the same signature in a derived class.
• Virtual functions allow for dynamic polymorphism in object-oriented programming.

• They are used to achieve runtime polymorphism by enabling late binding.

• Virtual functions are declared in a base class and can be overridden in derived classes.

• Example: v...read more
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Q2. Can you explain how to perform a level order traversal of a binary tree in spiral form?
Ans. 
Level order traversal of a binary tree in spiral form involves alternating between left and right while traversing each level.
• Start by pushing the root node into a queue.

• While the queue is not empty, pop a node, print its value, and push its children into the queue.

• For each level, alternate between popping nodes from the queue and printing their values from left to right or right to left.

• Continue this process until all
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Q3. What are abstract classes in C++?
Ans. 
Abstract classes in C++ are classes that cannot be instantiated and are designed to be base classes for other classes.
• Abstract classes may contain pure virtual functions, making them incomplete and unable to be instantiated.

• Derived classes must implement all pure virtual functions from the abstract class in order to be concrete classes.

• Abstract classes can have non-virtual functions and member variables like regular cl...read more
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Round duration - 60 minutes
Round difficulty - Easy

This was also a technical round. He asked to optimize the code I wrote in coding round. Then he asked me a few puzzles and questions on OOPS, OS and DBMS.

Q1. 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.
• ACID stands for Atomicity, Consistency, Isolation, and Durability.

• Atomicity ensures that either all operations in a transaction are completed successfully or none of them are.

• Consistency ensures that the database remains in a consistent state before and after the transaction.

• Isolation ensures that the e...read more
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Q2. What is the difference between paging and segmentation in operating systems?
Ans. 
Paging and segmentation are memory management techniques in operating systems.
• Paging divides physical memory into fixed-size blocks called pages, while segmentation divides logical memory into variable-size segments.

• Paging allows for efficient memory allocation and management, while segmentation provides protection and sharing of memory.

• Paging is simpler to implement but can lead to internal fragmentation, while segmen...read more
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Q3. What is concurrency control?
Ans. 
Concurrency control is a technique used in databases to manage simultaneous access and modification of data by multiple users or processes.
• Concurrency control ensures that transactions are executed in a way that maintains data consistency and integrity.

• Techniques like locking, timestamp ordering, and optimistic concurrency control are used to implement concurrency control.

• For example, in a banking system, concurrency c...read more
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Q4. What is the difference between String Buffer and String Builder in Java?
Ans. 
String Buffer is synchronized and thread-safe, while String Builder is not synchronized and faster.
• String Buffer is synchronized, making it thread-safe for use in multi-threaded environments.

• String Builder is not synchronized, resulting in faster performance but not thread-safe.

• String Builder is preferred for single-threaded operations, while String Buffer is preferred for multi-threaded operations.
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Q5. What are smart pointers in C++?
Ans. 
Smart pointers in C++ are objects that act like pointers but provide automatic memory management.
• Smart pointers help prevent memory leaks by automatically managing memory allocation and deallocation.

• Examples include unique_ptr, shared_ptr, and weak_ptr.

• unique_ptr is used for exclusive ownership, shared_ptr for shared ownership, and weak_ptr to prevent circular references.
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Q6. What is the difference between a mutex and a semaphore?
Ans. 
Mutex is used for exclusive access to a resource, while semaphore is used for controlling access to a resource by multiple threads.
• Mutex is binary and allows only one thread to access the resource at a time.

• Semaphore can have a count greater than one, allowing multiple threads to access the resource simultaneously.

• Mutex is typically used for protecting critical sections of code, while semaphore is used for synchronizat...read more
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Round duration - 60 minutes
Round difficulty - Easy

The second round is also written but you need to write programming based on their concept.

Q1. 
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 better efficiency

• Optimize by only checking up to the square root of N for divisors
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Q2. 
Palindrome String Validation
Determine if a given string 'S' is a palindrome, considering only alphanumeric characters and ignoring spaces and symbols.
Note:
The string 'S' should be evaluated in a case...read more
Ans. 
Check if a given string is a palindrome after removing special characters, spaces, and converting to lowercase.
• Remove special characters and spaces from the string

• Convert the string to lowercase

• Check if the modified string is a palindrome by comparing characters from start and end
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Round duration - 60 minutes
Round difficulty - Easy

Technical round with questions mainly on Java and OOPS concepts.

Q1. What is the difference between static methods and instance methods in Java?
Ans. 
Static methods belong to the class itself, while instance methods belong to individual objects of the class.
• Static methods are called using the class name, while instance methods are called using object references.

• Static methods cannot access instance variables directly, while instance methods can access both static and instance variables.

• Static methods are shared among all instances of the class, while instance method...read more
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Q2. What is the difference between an abstract class and an interface in Java?
Ans. 
Abstract class can have both abstract and non-abstract methods, while interface can only have abstract methods.
• Abstract class can have constructors, member variables, and methods with implementation.

• Interface can only have abstract methods and constants.

• A class can implement multiple interfaces but can only extend one abstract class.

• Example: Abstract class - Animal with abstract method 'eat', Interface - Flyable with m
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Q3. What is the difference between ClassNotFoundException and NoClassDefFoundError in Java?
Ans. 
ClassNotFoundException occurs when a class is not found during runtime, while NoClassDefFoundError occurs when a class was found during compilation but not during runtime.
• ClassNotFoundException is a checked exception, while NoClassDefFoundError is an Error.

• ClassNotFoundException occurs when a class is not found at runtime, usually due to a missing classpath or incorrect class name.

• NoClassDefFoundError occurs when a cla...read more
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Q4. What is the difference between an Error and an Exception in Java?
Ans. 
Error is a serious issue that cannot be handled at runtime, while Exception is a recoverable issue that can be caught and handled.
• Error is a subclass of Throwable and is usually caused by the environment or system, such as running out of memory or stack overflow.

• Exception is also a subclass of Throwable but is caused by the application code, such as invalid input or file not found.

• Errors are unchecked and are not meant...read more
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Q5. What is SerialVersionUID in Java?
Ans. 
SerialVersionUID is a unique identifier used by Java to ensure the compatibility of serialized objects.
• SerialVersionUID is a static final long variable in a class that implements Serializable interface.

• It is used to ensure that the serialized object can be deserialized correctly even if the class definition has changed.

• If the SerialVersionUID of the serialized object does not match the one in the class, an InvalidClass...read more
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Q6. What are the requirements for creating an immutable class in Java?
Ans. 
Requirements for creating an immutable class in Java
• Make the class final so it cannot be extended

• Make all fields private and final

• Do not provide setter methods, only getter methods

• Ensure that mutable objects are not returned in getter methods

• Override equals() and hashCode() methods for proper comparison

• Consider making defensive copies of mutable fields in constructor or getter methods
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