NowNow Interview Questions and Answers

An immutable class is a class whose instances cannot be modified after creation.

• Make all fields private and final

• Don't provide any setter methods

• Ensure that any mutable objects passed to the constructor are defensively copied

• Make the class final so that it cannot be subclassed

Singleton pattern ensures only one instance of a class is created and provides a global point of access to it.

• Create a private constructor to prevent direct instantiation of the class.

• Create a private static instance of the class.

• Create a public static method to access the instance, and create the instance if it doesn't exist.

• Ensure thread safety by using synchronized keyword or double-checked locking.

Vector is synchronized and ArrayList is not. Vector is thread-safe and ArrayList is not.

• Vector is a legacy class and ArrayList is a part of the Java Collection Framework.

• Vector is synchronized which means only one thread can access it at a time, while ArrayList is not.

• Vector is thread-safe which means it can be used in a multi-threaded environment, while ArrayList is not.

• Vector is slower than ArrayList because of synch...read more

Create Linked List without using internal library and provide add, delete, find functionality.

• Create a Node class with data and next pointer

• Create a LinkedList class with head pointer and methods to add, delete, and find nodes

• Use a loop to traverse the list and perform operations

• Handle edge cases such as adding to an empty list or deleting the head node

The current system follows a microservices architecture.

• The system is divided into multiple independent services.

• Each service has its own database and communicates with other services through APIs.

• The architecture allows for scalability and flexibility.

• Examples of microservices used in the system include user authentication, payment processing, and inventory management.

Find the total no of islands in a 2D matrix.

• Use DFS or BFS to traverse the matrix.

• Mark visited cells to avoid repetition.

• Count the number of islands found.

Loop detection in a linked list.

• Use two pointers, one moving at twice the speed of the other.

• If there is a loop, the faster pointer will eventually catch up to the slower one.

• If there is no loop, the faster pointer will reach the end of the list.

Merge Sort is a divide and conquer algorithm that sorts an array by dividing it into two halves, sorting them separately, and then merging the sorted halves.

• Divide the array into two halves

• Recursively sort the two halves

• Merge the sorted halves

Find pairs of integers in a BST whose sum is equal to a given number.

• Traverse the BST and store the values in a hash set.

• For each node, check if (X - node.value) exists in the hash set.

• If yes, add the pair (node.value, X - node.value) to the result.

• Continue traversal until all nodes are processed.

Merge overlapping time intervals into mutually exclusive intervals.

• Sort the intervals based on their start time.

• Iterate through the intervals and merge overlapping intervals.

• Output the mutually exclusive intervals.

• Example: [(1,3), (2,6), (8,10), (15,18)] -> [(1,6), (8,10), (15,18)]

Different types of hashing and alternative for Linear Chaining

• Different types of hashing include division, multiplication, and universal hashing

• Alternative for Linear Chaining is Open Addressing

• Open Addressing includes Linear Probing, Quadratic Probing, and Double Hashing

An AVL tree is a self-balancing binary search tree where the heights of the left and right subtrees differ by at most one.

• AVL tree is a binary search tree with additional balance factor for each node.

• The balance factor is the difference between the heights of the left and right subtrees.

• Insertion and deletion operations in AVL tree maintain the balance factor to ensure the tree remains balanced.

• Rotations are performed ...read more

Find the minimum number of squares whose sum equals to a given number n.

• Use dynamic programming to solve the problem efficiently.

• Start with finding the square root of n and check if it is a perfect square.

• If not, then try to find the minimum number of squares required for the remaining number.

• Repeat the process until the remaining number becomes 0.

• Return the minimum number of squares required for the given number n.

Insertion sort for a singly linked list.

• Traverse the list and compare each node with the previous nodes

• If the current node is smaller, swap it with the previous node

• Repeat until the end of the list is reached

• Time complexity is O(n^2)