First Round: DSA and Algorithms Basic DSA Concepts What is a data structure, and why is it used? Non-Linear Data Structures Explain a non-linear data structure. Sorting Techniques Explain a sorting algorithm. Divide and Conquer Explain the divide and conquer algorithm. Priority Queue Explain priority queues and their use cases. Deque (Double-Ended Queue) What is a deque, and how does it work? Basic SQL Concepts WHERE Clause What is the use of the WHERE clause? WHERE vs. HAVING Clause Explain the difference between WHERE and HAVING clauses. Second Round: System Design After the first round, a HackerRank link is shared for coding with an invite. Payment Aggregation Given different payment types and corresponding amounts (e.g., {credit card: 400, UPI: 200}), write a function to return the total amount for each payment type. Notification System Design Design a scalable notification system.