PayU Payments Senior Software Engineer Interview Questions and Answers

Implement thread safe load balancer.
focus on input validations and cover all corner cases in tests

Q1. Explain Concurrency
Ans. 
Concurrency is the ability of a system to execute multiple tasks simultaneously.
• Concurrency allows multiple tasks to run concurrently, improving performance and efficiency.

• Concurrency can be achieved through multithreading or multiprocessing.

• Example: A web server handling multiple requests simultaneously using multithreading.
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Q2. Explain Acid principles
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ACID principles are a set of properties that guarantee database transactions are processed reliably.
• Atomicity: Transactions are all or nothing. If one part of the transaction fails, the entire transaction is rolled back.

• Consistency: Transactions bring the database from one valid state to another. All constraints are satisfied.

• Isolation: Transactions are isolated from each other until they are completed.

• Durability: Once...read more
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Q1. Low Level Design: How to do rate limiting for a platform serving 100K requests per second.
Ans. 
Implement rate limiting for a platform serving 100K requests per second.
• Use a token bucket algorithm to limit the rate of incoming requests.

• Set a maximum number of tokens in the bucket to control the rate.

• Refill the bucket at a constant rate to allow bursts of requests.

• Track the timestamp of the last request to enforce the rate limit.

• Consider using a distributed rate limiting system for scalability.

• Monitor and adjust t...read more
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Q1. Easy question from leetcode.
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Q1. Just normal questions based on resume and previous projects
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Codility Test with leetcode medium questions

Q1. Built a react feature
Ans. 
Built a react feature
• Identify the specific feature to be built

• Design the component hierarchy and state management

• Implement the feature using React components and hooks

• Test the feature for functionality and user experience

• Refactor and optimize the code for performance
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Q2. Questions based around react
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Q3. How to implement timer
Ans. 
A timer can be implemented using a combination of system time and a loop that checks for elapsed time.
• Get the current system time at the start of the timer

• Enter a loop that continuously checks the difference between the current system time and the start time

• When the desired time has elapsed, perform the desired action or trigger an event
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Q4. How to implement useEffect
Ans. 
useEffect is a hook in React that allows you to perform side effects in functional components.
• useEffect is used to handle side effects in React components.

• It takes two arguments: a function and an optional array of dependencies.

• The function inside useEffect is executed after the component renders.

• The optional array of dependencies determines when the effect should run.

• If the array of dependencies is empty, the effect r...read more
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Q1. Given two sorted arrays, a (m elements, size m+n) and b (n elements, size n) merge both the arrays into the first array a.
Ans. 
Merge two sorted arrays into the first array
• Start from the end of both arrays and compare elements

• Place the larger element at the end of the first array

• Continue this process until all elements are merged
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Q2. Given a monolith architecture, how would you scale it to handle 3x the traffic and also improve response time on API's during peak hours by using cache
Ans. 
To scale a monolith architecture and improve response time, use horizontal scaling and implement caching.
• Implement horizontal scaling by adding more instances of the monolith application behind a load balancer

• Use a distributed cache to store frequently accessed data and reduce database queries

• Implement caching at different levels such as application-level caching, database query caching, and HTTP response caching

• Use a ...read more
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Q3. Class design for a cache implementation, implement get(), put(), initialization methods
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Design a cache class with get(), put(), and initialization methods.
• Define a class with a data structure to store key-value pairs.

• Implement a get() method to retrieve a value from the cache based on a given key.

• Implement a put() method to add or update a key-value pair in the cache.

• Implement an initialization method to set the initial capacity and eviction policy of the cache.

• Consider using a hash map or a linked list t...read more
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