Paytm Interview Experince for Software Engineer | 2+ Years Experienced

I applied on Instahyre and shared my resume. HR called me and setup the whole process. HR was very helpful throughout the whole process.  

Online Round(70 minutes): This round has 4 sections

• One Coding question: Longest Collatz sequence
• JAVA MCQs
• SQL MCQs
• Data Structure MCQs

Technical Round 1(1 hour):

• Median of Two Sorted Arrays –  I was able to give the solution using extra space, but stuck with Constant space complexity.
• Design a stack that supports getMin() in O(1) time and O(1) extra space – I shared my approach, he was satisfied with my approach and asked me to code it in any language.
• Questions on Multi – threading in Java
• Questions on Collections – HashMap, ConcurrentHashMap

Technical Round 2(1 hour):

• Find duplicates in constant array with elements 0 to N-1 in O(1) space  – I solved it fully with code
• Print even and odd numbers in increasing order using two threads in Java – wasn’t able to code it completely but I shared the approach using ‘Synchronized’ functions.
• Different between Wait(), notify() and notifyAll() in java. Give real world examples.
• Some more questions in Multi threading in Java.

Technical Round 3(1 hour):

• Largest Sum Contiguous Subarray – I solved it fully with code.
• Maximum cost path in an Undirected Graph such that no edge is visited twice in a row. – Shared the approach. He asked to improve the time complexity. I partially came up with the solution.
• Java OOPS Concept with Example.
• Diamond problem in C++.
• Difference between HashTable and HashMap.
• How LinkedHashMap maintain insertion order? Is it thread-safe? – wasn’t able to provide proper answer as I was only aware of HashMap internal working.
• How ConcurrentHashMap is different than HashMap? Tell me the implementation of ConcurrentHashMap.  –
• Synchronized keyword in Java

Technical/Managerial Round (1 hour):

• Brief introduction of me.
• What is the architecture of the project the one I am working in my present company? What is my role? How you handled conflicts in the project?
• System Design Questions
• How would you consume Paytm APIs in your restaurant to give cashback to your users in Paytm?
• How would you design Campaign APis for online food application like swiggy to give users discounts using Locations of the users?
• Immutable in Java. How can we create a immutable class in Java

I was rejected after final round. 

• I was stuck in some System Design cross questions. In this round they want to know how you are working in your current organization. What are your roles in the project. How you contributed to solve the problems in your projects.
• If I evaluate myself then I was rejected because of lack of knowledge of internal working of Collections in Java. But I enjoyed the whole process and all the interviewers were very nice and helpful. Please be yourself and try to think out loud in the interview. Ask for help if you stuck in any problem.  
• Brush up Multithreading, Concurrency, Internal working of Collections in Java.

Good luck!!