Round 1: Find the loop in Linked List. Find LCA in the tree. Round 2: Find the submatrix having the max sum in the matrix. This question was tricky but good. Round 3(assignment): Make parallel calls and scrap data from e-commerce websites. Round 4: Write a function in Python to serialize an array to a string having no restrictions on input and a function to deserialize a string to an array without using any library. It was quite difficult to understand and the interviewer looked like had no interest in the interview. Singleton vs factory design pattern. Why use class in singleton instead of object or function.