Paytm Interview Experience – On Campus

Paytm visited our campus for the post of Software Engineer. The interview process consisted of following rounds.

Online Round: The online round consisted of 3 programming questions. The test was conducted on cocubes.

• Given two strings A and B, transform one string into another. The only allowed operation was to put any character from string A and place it at the beginning of the string. You have to output minimum no. of operations required if it is possible, else print “-1”.
  https://www.geeksforgeeks.org/transform-one-string-to-another-using-minimum-number-of-given-operation/
• Given a range of numbers [L, R]. Find out the count of numbers whose sum of digits is prime.
• Given a matrix representing which child likes which toy.
  matrix[i][j]=1 represents that child i likes toy j. One child can get only 1 toy and one toy can be assigned to only 1 child. Find the maximum number of children who can get the toy they wished.

38 students were shortlisted for the interviews.

Round 1 (Technical): The interview asked me the following problems, after listening to my approach, he asked me to write code for the problems.

• Find no. of unique elements in every window of size k in an array.
  https://www.geeksforgeeks.org/count-distinct-elements-in-every-window-of-size-k/
• Given a binary tree, he asked me to print the elements of the tree in the following way:-
  Print first two levels of the tree from left to right, and the next two levels from right to left and so on.

After answering these two problems, he asked me a design problem and discussed thoroughly the various approaches to deal with the situation.

I was shortlisted for the next round.

Round 2 (Technical): In this round, I was asked questions on core OS, DBMS along with Data structures. The interviewer was friendly in nature. He asked me the following questions:

• Write a program for Tower of Hanoi problems.
  https://www.geeksforgeeks.org/c-program-for-tower-of-hanoi/
• Implement a stack using queue.
  https://www.geeksforgeeks.org/implement-stack-using-queue/
  I first gave him a solution using priority_queue, to which he said that he wants to use a simple queue.
• Print the bottom view of binary tree.
  https://www.geeksforgeeks.org/bottom-view-binary-tree/
  After listening the approach, he asked me to write code for all the problems he asked.
• He asked me about work I have done during my internship and why I have used some specific python modules for doing a particular task.
• Then he asked me about ACID property of DBMS and discussion about insert and delete anomalies.
• He asked me about deadlock, race condition, mutex and asked me to write code to demonstrate how race condition occurs and how to deal with it.

Round 3 (Technical): This round was taken by the AVP-engineering. He first asked me about OOPS, and then gave me a programming question.

• Write a recursive code to print a matrix in spiral order.

He then asked me to design a database for the movie review system in which users can comment, upvote, and reply to comments for movies along with giving ratings and reviews. The database was to be designed such that there are least insertion and deletion anomalies.

He then asked me about the work that I have done during my internship.

HR Round: The HR first asked me to introduce myself. She asked me why I want to join Paytm and asked me to explain my B.tech project. Then she asked me many behavioral questions. She told me about the work culture at Paytm, and finally, she asked if I had any queries.

Verdict – Selected.

I would suggest you to discuss your approach with the interviewer because they are basically looking for how you approach a problem and how to come up with an answer i.e. your thought process while formulating the solution to the problem.