10+ Walstar Technologies Interview Questions and Answers

Find all triplets in an array of integers without duplicates

• Iterate through the array and for each element, find all pairs that sum up to the negative of that element

• Use a set to store the seen elements to avoid duplicates

• Time complexity can be improved to O(n^2) by sorting the array first

To find all square matrices in a given matrix, iterate through each cell as the top left corner of a potential square matrix and check if all elements within the square are the same.

• Iterate through each cell in the matrix as the top left corner of a potential square matrix

• For each cell, check if all elements within the square formed by the cell are the same

• If all elements are the same, consider it as a square matrix

Loop through the linked list to find and remove a specific node

• Start at the head of the linked list and iterate through each node

• Check if the current node matches the one to be removed

• If found, update the pointers to skip over the node and remove it

• Continue until the end of the list is reached

The question is asking to calculate the number of hops an elevator needs to travel between floors.

• Calculate the difference between the starting floor and the destination floor

• Divide the difference by the maximum number of floors the elevator can travel in one hop

• Round up the result to get the number of hops needed

Implementing hashmap in Java

• Create an array of linked lists to store key-value pairs

• Hash the key to get the index of the array

• Insert the key-value pair at the index in the linked list

• Handle collisions by chaining

• Implement methods like put(), get(), remove()

• Use generics to allow any type of key-value pairs

Transactions in Spring Boot manage database transactions in a declarative way.

• Spring Boot uses @Transactional annotation to mark a method as transactional.

• Transactions can be managed at class level or method level.

• Rollback can be configured based on specific exceptions.

• Example: @Transactional(propagation = Propagation.REQUIRED, rollbackFor = Exception.class)