PAJASA Apartments Interview Questions and Answers

Round duration - 90 minutes
Round difficulty - Medium

Coding question of medium level difficulty, from DP. 
18 MCQs were core CSE related concepts e.g: OS, OOPs, DBMS, Networking
Time was 90 minutes.

Q1. 
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.
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Round duration - 30 minutes
Round difficulty - Medium

It was an one-to-one interview. It checks your problem solving ability and a few OOPs, OS, DBMS etc concepts. Coding questions were related to array, queue and DP.

Q1. 
Triangle Formation Using Array Elements
Given an integer array/list ARR of length 'N', determine if it is possible to form at least one non-degenerate triangle using the values of the array as the sides o...read more
Ans. 
Determine if it is possible to form a non-degenerate triangle using array elements as sides.
• Check if the sum of any two sides is greater than the third side for all combinations of sides.

• If the above condition is met for any combination, return true; otherwise, return false.
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Q2. 
Maximum Sum of Non-Adjacent Elements
You are given an array/list of integers. The task is to return the maximum sum of a subsequence such that no two elements in the subsequence are adjacent in the given ...read more
Ans. 
Find the maximum sum of non-adjacent elements in an array.
• Use dynamic programming to keep track of the maximum sum at each index, considering whether to include the current element or not.

• At each index, the maximum sum can be either the sum excluding the current element or the sum including the current element but excluding the previous element.

• Iterate through the array and update the maximum sum accordingly.

• Example: F...read more
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Round duration - 45 minutes
Round difficulty - Easy

It was also a problem solving round. However after coding questions, they also asked CSE conceptual questions.

Q1. 
Sum Tree Conversion
Convert a given binary tree into its sum tree. In a sum tree, every node's value is replaced with the sum of its immediate children's values. Leaf nodes are set to 0. Finally, return th...read more
Ans. 
Convert a binary tree into a sum tree by replacing each node's value with the sum of its children's values. Return preorder traversal.
• Traverse the tree in a bottom-up manner, starting from the leaf nodes.

• For each node, update its value to the sum of its children's values.

• Set leaf nodes to 0.

• Return the preorder traversal of the modified tree.
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Q2. What are the core concepts of indexing in Database Management Systems (DBMS)?
Ans. 
Core concepts of indexing in DBMS include types of indexes, benefits of indexing, and factors affecting index performance.
• Types of indexes: B-tree, Hash, Bitmap, etc.

• Benefits of indexing: Faster data retrieval, improved query performance, reduced disk I/O.

• Factors affecting index performance: Selectivity, clustering factor, index fragmentation.

• Examples: Creating an index on a column in a table to speed up search queries
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There was a scenario given where there is a plane crash and we survived and few things were with us , so how we use those things for survival after the crash in an unknown place.

Q1. Asked about myself.. and asked about my role model and vision for the future.
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Its contain a simple task of crud operation.

Q1. Behavior question. and salary discussion
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Q2. General discussion with hr
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Q3. Are you comfortable with 2 years of the bond?
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Q1. Have you worked on pg ?
Ans. 
Yes, I have worked on pg.
• I have experience working with PostgreSQL, commonly referred to as pg.

• I have worked on designing and implementing database schemas using pg.

• I have also written complex SQL queries and optimized them for performance using pg.

• In addition, I have experience with pgAdmin, a popular GUI tool for managing PostgreSQL databases.
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Q2. What is difference between session and cookie?
Ans. 
Session is stored on server side while cookie is stored on client side.
• Session is a server-side storage mechanism that stores user-specific data for a specific period of time.

• Cookie is a client-side storage mechanism that stores user-specific data in the user's browser.

• Session data is stored on the server and is not accessible by the client, while cookie data is stored on the client and can be accessed by the client.

• Se...read more
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Q1. Explain the difference between ArrayList and LinkedList in Java. When would you choose one over the other?
Ans. 
ArrayList is a resizable array, while LinkedList is a doubly linked list. Choose based on performance needs.
• ArrayList: Faster for random access (O(1)). Example: list.get(5);

• LinkedList: Faster for insertions/deletions (O(1)) at both ends. Example: list.addFirst('A');

• ArrayList: Uses less memory overhead compared to LinkedList.

• LinkedList: Better for frequent insertions/deletions in the middle of the list.

• ArrayList: Requir...read more
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Q2. What are the advantages and disadvantages of using Java’s synchronized keyword for thread synchronization? Can you explain how the ReentrantLock compares to synchronized?
Ans. 
Java's synchronized keyword provides thread safety but has limitations compared to ReentrantLock.
• Advantages of synchronized: Simple to use, built-in language feature.

• Disadvantages of synchronized: Can lead to thread contention, no timeout options.

• ReentrantLock allows more flexibility: supports tryLock(), lockInterruptibly().

• ReentrantLock can be more efficient in high contention scenarios.

• Example of synchronized: synchr...read more
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Q3. What is the difference between == and .equals() in Java? When should each be used, and what issues can arise from improper usage?
Ans. 
== checks reference equality, while .equals() checks value equality in Java. Use .equals() for content comparison.
• == compares object references (memory addresses). Example: String a = new String('test'); String b = new String('test'); a == b returns false.

• .equals() compares actual content of objects. Example: a.equals(b) returns true.

• Use == for primitive types (int, char, etc.) and .equals() for objects.

• Improper use of...read more
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Q4. How does the Java garbage collector work? Can you describe the different types of garbage collection algorithms available in Java?
Ans. 
Java's garbage collector automatically manages memory by reclaiming unused objects, improving performance and preventing memory leaks.
• Garbage Collection (GC) is the process of automatically identifying and disposing of objects that are no longer needed.

• Java uses several GC algorithms, including Serial, Parallel, CMS (Concurrent Mark-Sweep), and G1 (Garbage-First).

• The Serial GC is a simple, single-threaded collector sui...read more
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Q5. What are the main features of Java 8? Can you explain how lambdas and the Stream API have changed the way Java applications are written?
Ans. 
Java 8 introduced lambdas, Stream API, and other features that enhance functional programming and improve code readability.
• Lambdas: Enable concise representation of functional interfaces. Example: (x, y) -> x + y.

• Stream API: Allows processing sequences of elements (collections) in a functional style. Example: list.stream().filter(x -> x > 10).collect(Collectors.toList()).

• Default Methods: Interfaces can have me...read more
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Q6. Describe the differences between checked and unchecked exceptions in Java. Provide examples and explain how to handle them properly.
Ans. 
Checked exceptions must be declared or handled; unchecked exceptions do not require explicit handling.
• Checked exceptions are subclasses of Exception but not of RuntimeException.

• Example of checked exception: IOException, which must be caught or declared.

• Unchecked exceptions are subclasses of RuntimeException.

• Example of unchecked exception: NullPointerException, which does not need to be declared.

• Checked exceptions are t...read more
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Q7. What is the Java Memory Model, and how does it affect multithreading and synchronization? How does volatile help ensure memory visibility?
Ans. 
The Java Memory Model defines how threads interact through memory, ensuring visibility and ordering of shared variables.
• The Java Memory Model (JMM) specifies how threads interact with memory, ensuring consistency and visibility of shared variables.

• It defines rules for visibility, atomicity, and ordering of operations in a multithreaded environment.

• Without proper synchronization, threads may see stale or inconsistent da...read more
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Q8. Can you explain the difference between method overloading and method overriding in Java? Provide examples where each should be used.
Ans. 
Method overloading allows multiple methods with the same name but different parameters; overriding allows subclass methods to replace superclass methods.
• Method Overloading: Same method name, different parameter types or counts.

• Example of Overloading: 'int add(int a, int b)' and 'double add(double a, double b)'.

• Use Overloading for convenience and readability when performing similar operations.

• Method Overriding: Same met...read more
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Q9. What are functional interfaces in Java? How do they work with lambda expressions? Provide an example of a custom functional interface.
Ans. 
Functional interfaces in Java are interfaces with a single abstract method, enabling lambda expressions for concise code.
• A functional interface has exactly one abstract method.

• They can have multiple default or static methods.

• Common examples include Runnable, Callable, and Comparator.

• Lambda expressions provide a clear and concise way to implement functional interfaces.

• Example of a custom functional interface: @Functiona...read more
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Q10. What is a Java Stream, and how does it differ from an Iterator? Explain how Streams can be used to process collections efficiently.
Ans. 
Java Streams provide a functional approach to processing sequences of elements, unlike Iterators which are imperative.
• Streams are part of the Java 8+ API, enabling functional-style operations on collections.

• Unlike Iterators, Streams do not store data; they process data on-the-fly.

• Streams support operations like map, filter, and reduce, allowing for concise and readable code.

• Example: List<String> names = Arrays.as...read more
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Q11. Explain the concept of immutability in Java. How does the String class achieve immutability, and what are the advantages of immutable objects?
Ans. 
Immutability in Java means objects cannot be modified after creation, enhancing security and performance.
• 1. Immutability: Once created, an object's state cannot be changed.

• 2. String Class: Strings in Java are immutable; any modification creates a new String object.

• 3. Example: String s1 = "Hello"; s1 = s1 + " World!"; // s1 now points to a new String object.

• 4. Advantages: Thread-safe, easier to cache, and can be used as...read more
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Q12. What is the difference between final, finally, and finalize in Java? Provide examples to illustrate their usage.
Ans. 
final, finally, and finalize serve different purposes in Java: variable declaration, exception handling, and garbage collection respectively.
• final: Used to declare constants. Example: final int MAX_VALUE = 100;

• finally: Block that executes after try-catch, regardless of exceptions. Example: try { ... } catch { ... } finally { ... }

• finalize: Method called by the garbage collector before an object is removed. Example: pro
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Q13. Explain the Singleton design pattern in Java. How can you implement it safely to ensure thread safety?
Ans. 
The Singleton pattern restricts instantiation of a class to one object, ensuring controlled access to that instance.
• 1. The Singleton pattern ensures a class has only one instance and provides a global point of access to it.

• 2. Common implementations include lazy initialization, eager initialization, and double-checked locking.

• 3. Lazy initialization: Create the instance when it is needed, using synchronized method for th...read more
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Q14. What are Java annotations, and how are they used in frameworks like Spring? Explain the difference between built-in and custom annotations.
Ans. 
Java annotations provide metadata for classes, methods, and fields, enhancing functionality in frameworks like Spring.
• Annotations are metadata that provide information about the program but are not part of the program itself.

• In Spring, annotations like @Component, @Service, and @Controller are used for defining beans and their roles.

• Built-in annotations include @Override, @Deprecated, and @SuppressWarnings, which serve...read more
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Q15. How do Java Streams handle parallel processing? What are the potential pitfalls of using parallel streams, and how can they be mitigated?
Ans. 
Java Streams enable parallel processing for efficient data handling but come with potential pitfalls that need careful management.
• Java Streams can be processed in parallel using the 'parallelStream()' method, which divides the workload across multiple threads.

• Parallel streams utilize the Fork/Join framework, allowing tasks to be split and executed concurrently, improving performance for large datasets.

• Potential pitfall...read more
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Q16. Explain the difference between ArrayList and LinkedList in Java. ArrayList is implemented as a dynamic array, while LinkedList is a doubly linked list. ArrayList provides fast random access (O(1) complexi...read more
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Q17. What are the advantages and disadvantages of using Java’s synchronized keyword for thread synchronization? The synchronized keyword ensures that only one thread can access a block of code at a time. It pr...read more
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Q18. What is the difference between == and .equals() in Java? == checks for reference equality, meaning it compares memory addresses. equals() checks for value equality, which can be overridden in user-defined...read more
Ans. 
== checks reference equality; .equals() checks value equality, can be overridden for custom comparison.
• == compares memory addresses: new String("hello") == new String("hello") returns false.

• .equals() compares actual content: "hello".equals("hello") returns true.

• Override equals() when logical equality differs from reference equality, e.g., in custom classes.

• When overriding equals(), also override hashCode() to maintain ...read more
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Q19. How does the Java garbage collector work? Garbage collection in Java automatically reclaims memory occupied by unused objects. The JVM has different types of GC algorithms, including Serial, Parallel, CMS...read more
Ans. 
Java's garbage collector automatically manages memory, reclaiming space from unused objects through various algorithms.
• Garbage collection in Java is automatic, freeing developers from manual memory management.

• The JVM uses different GC algorithms: Serial, Parallel, CMS, and G1, each with unique characteristics.

• Memory is divided into Young Generation (short-lived objects) and Old Generation (long-lived objects).

• Minor GC ...read more
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Q20. What are the main features of Java 8? Java 8 introduced lambda expressions, enabling functional-style programming. The Stream API allows efficient data processing with map, filter, and reduce operations. ...read more
Ans. 
Lambda expressions enhance Java code readability and maintainability by simplifying syntax and promoting functional programming.
• Concise Syntax: Lambda expressions reduce boilerplate code. For example, instead of writing an anonymous class for a Runnable, you can use: `Runnable r = () -> System.out.println("Hello");`

• Improved Readability: Code becomes more expressive. For instance, using `list.forEach(item -> Syste...read more
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Q1. DSA & Java stream
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Q1. System design round
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Q1. Basic about past experience
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