Backend Engineer | PayPay

Current YOE : 4 Current Organisation : PBC TC : 26 Base + 10% Var

First Round (60 mins): The interviewer seemed really nice the first 30 mins asked about the most challenging project dug deeper on the same, asked me about the different concepts like REST APIs, SQL vs NoSQL etc and some java concepts. The last 30 mins was DSA question where they asked this question : Given an input in this format : [fileID, CollectionId, fileSize] find the topK collections based on their size of files inside them. The filesystem was like this - FileSystem contains Collection which in turn contains Files. Gave the heap approach selected for the next round.

Second Round (60 mins) : Asked me about a few questions based on my resume, then gave a Graph question : https://leetcode.com/problems/min-cost-to-connect-all-points/description/ . Post this we had a discussion related to API design and LLD of a notification system (Was just asked how would I approach this not asked to code it like which design pattern would you use given a certain scenario.)

Third Round (60 mins) : System Design Round was asked to Design a PasteBin Service asked the FR and the NFR they were as follows -

- 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 open the same and see the contents of the file.
- The amount of time the file should persist should be customisable but at max 6 months.
- Around 600 M monthly active users should be handled.

My Approach : I proposed a 2 step design - Storage service and then URL generation service. But was not able to answer questions like how much compute qould be required in case 100 concurrent users upload 5GB files or how would we handle the larger files should we chunk it? What compute would be required in that case. I think I was wrong from the get go itself in generating the URLs and then uploading a file or first uploading a file and then generating the URL.

Verdict : Rejected Hope it helps.