35 questions · from 4 interviews
Paypay interview questions
Every question candidates reported from their Paypay interviews, most frequently asked first. Each links to the write-up it came from, so you can see the round and how it went.
Paypay coding and DSA questions
- 01
Next Greatest Element in Circular Array
Given a circular array of integers, for each element find the next greater element in the order of traversal. If no greater element exists, output -1 for that position.
Medium · From PayPay | Backend Engineer | Interview Experience | Sepetember 2026
- 02
BST Time Complexity
Discussed the time complexity for insertion and accessing an element in a Binary Search Tree (BST).
- 03
Max Consecutive Ones III
Given a binary array nums and an integer k, return the maximum number of consecutive 1's in the array if you can flip at most k 0's.
Medium · From PayPay || SDE 2 || Interview Experience || Feb 2026
- 04
Maximum Path Sum in Binary Tree
Find the maximum path sum in any tree on a downward path. Follow-up: what if the path can be in any direction, not necessarily downwards?
Hard · From PayPay || SDE 2 || Interview Experience || Feb 2026
- 05
Top K Collections by File Size
Given an input in this format: [fileID, CollectionId, fileSize] . Find the top K collections based on their size of files inside them. The filesystem was like this - FileSystem contains Collection which in turn contains Files.
- 06
- 07
Number of Adjacent Elements with the Same Color (Modified)
A LeetCode problem (Number of Adjacent Elements with the Same Color) was asked, with different constraints.
From PayPay | Japan | June 2025 | Backend Engineer | Interview Experience[Rejected]
- 08
SkipList Data Structure
Discussion on SkipList Data structure: working and time complexity of insert, delete operations.
From PayPay | Japan | June 2025 | Backend Engineer | Interview Experience[Rejected]
- 09
Bloom Filter Deletion and Alternatives
Question on Bloom Filter: how to delete elements from a Bloom Filter. Follow-up: which data structure similar to Bloom Filter supports deletion (e.g., Cuckoo Filter).
From PayPay | Japan | June 2025 | Backend Engineer | Interview Experience[Rejected]
- 10
Bellman-Ford Algorithm
Question on Bellman-Ford Algorithm: working and Time Complexity.
From PayPay | Japan | June 2025 | Backend Engineer | Interview Experience[Rejected]
- 11
Add Edges to Make Degrees of All Nodes Even
A LeetCode Hard problem (Add Edges to Make Degrees of All Nodes Even) was given, with working code expected in 20 minutes.
Hard · From PayPay | Japan | June 2025 | Backend Engineer | Interview Experience[Rejected]
Paypay system design questions
- 01
Database Selection & Comparison
Discussed database choices in projects, reasons for SQL over NoSQL, and the differences between SQL and NoSQL databases.
- 02
NoSQL Scalability & Distributed Systems Concepts
Explanation of how NoSQL supports horizontal scalability. Discussion on ACID properties and the CAP theorem. Whether consistency and availability are simultaneously possible.
- 03
SQL Database Isolation Levels & Indexing
Discussion on isolation levels and indices in SQL databases, including their advantages and disadvantages.
- 04
API Idempotency & HTTP Methods
What is idempotency in APIs and how can it be achieved? Difference between HTTP PUT and PATCH methods.
- 05
Optimistic vs. Pessimistic Locking
Discussed the difference between optimistic and pessimistic locking mechanisms.
- 06
Preventing Double Payments in Payment System
Discussed API design strategies to prevent double payments by a user in a payment system.
- 07
Handling Concurrent Actions from Multiple Devices
Discussed how to handle a scenario where a user performs an action (e.g., ticket booking) from multiple devices, ensuring it's reflected only once.
- 08
Redis Cache Exhaustion Handling
Discussed strategies and actions to take if Redis cache memory is exhausted.
- 09
Low-Level Design (LLD) of Ticket Master Website
Detailed discussion on the Low-Level Design (LLD) of a Ticket Master-like website, covering requirements specification, entity modeling, database schema design, and API design.
- 10
High-Level Design (HLD) of a System
Discussion on the High-Level Design (HLD) of a system.
- 11
Handling Concurrent Bookings
Discussed strategies for handling concurrent bookings in a system.
- 12
Database Indexing Strategy
Discussed criteria and scenarios for introducing indexing in database tables.
- 13
Optimizing Metadata Search & ElasticSearch Sync
Discussed methods to make searching of metadata faster and how ElasticSearch syncs with a primary database.
- 14
API Design and LLD of a Notification System
Discussion related to API design and low-level design (LLD) of a notification system. I was asked how I would approach this, focusing on design patterns for a given scenario, not asked to code.
- 15
Design a PasteBin Service
Design a PasteBin Service with the following functional and non-functional requirements: The user should be able to paste code/file (upto 5GB) in the service and should then get a URL. This URL should be sharable and then should allow anyone receiving it to…
- 16
Payment System: Handling Multiple Clicks
Scenario-based question: How to handle multiple pay clicks by a user in a payment system.
From PayPay | Japan | June 2025 | Backend Engineer | Interview Experience[Rejected]
Paypay behavioural and HR questions
- 01
Handling Critical Negative Feedback
Behavioral question: Describe a situation where you received critical negative feedback and how you handled it.
- 02
Pushing Limits
Behavioral question: Describe a situation where you pushed your limits.
- 03
Handling Team Disagreements
Behavioral question: Describe a situation where you had a disagreement with teammates and how you resolved it.
- 04
Reason for Switch & Role Expectations
Behavioral question: Discussed reasons for switching jobs and expectations for the new role.
Paypay other questions
- 01
Project Optimization Techniques
Discussed how I optimized the running time of my projects.
- 02
Sync vs Async Programming Internals
Question on Sync vs Async Programming, specifically how async/await works internally.
From PayPay | Japan | June 2025 | Backend Engineer | Interview Experience[Rejected]
- 03
Python Generators
Question on Generators in Python.
From PayPay | Japan | June 2025 | Backend Engineer | Interview Experience[Rejected]
- 04
JIT Compilation in Java
Question on JIT compilation in Java, working in depth.
From PayPay | Japan | June 2025 | Backend Engineer | Interview Experience[Rejected]
Paypay interview questions FAQ
What questions are asked in Paypay interviews?
Candidates reported 35 distinct questions across 4 Paypay interviews. 11 coding and DSA questions, 16 system design questions, 4 behavioural and HR questions, 4 other questions.