PayPal Data Engineer Interview Questions and Answers

Round: Test
Experience: The test was on hackerrank.
Tips: * Fast coding and problem solving required
* Time crunch
* The test is valued a LOT in the hiring process
Duration: 120 minutes
Total Questions: 4

Round: Technical Interview
Experience: Question 1 : He tried to take the discussion to web based technologies to which I straightly told I don’t know. Not sure if that was a good decision. Nevertheless, he went over my resume a lot of times and asked about various projects.
Question 2 : Discussed the various projects related to it.
Question 3 : He asked this question because I had worked on django during my FB internship. I proposed a tree based structure. xyz.com/a/b/c ---> b is child of a, c is child of b.

Question 4 : Next he moved to a very interesting question. Given a simple text editor, I want to facilitate autocomplete feature. We discussed about syntactic methods using language specific keywords. I suggested a trie based implementation which he liked. Later he asked me to improve and redirected me to using scope of the variables, and grammar of the language. We discussed about all the steps I did in language translators lab (macrojava -> minijava -> typechecking -> miniIR -> microIR -> miniRA ->Mips) where we built a Java compiler in Java. We later hopped back to original question and I suggested that we can use grammar to to store multiple (nested kind of) tries for different scope. He asked me how would I define “scope”. He gave me a scenario which helped me come up with the nested trie structure
int a;
{
int b;
{
int c; //a b c can be used
}
{
int d; //a b d can be used
}
}
He then asked me details of how I would code. I said we could use the respective visitors and maintain the current trie root for scope. He liked it but I missed at 2 places :
1. He asked me about token generation used in a compiler and I said flex and bison. I was expected to elaborate a bit.
2. He asked me how the grammar is generated and how the visitors are invoked. I couldn’t explain properly because I was not thorough with it.
Tips: * Keep smiling in the interviews.
* My interviewer had hopped from Microsoft to Visa. We had a short detailed discussion on how the transition was and what drove him to do that.
* It’s always good to know about the company to pick up interesting discussions, read up latest articles and news
* The interviewers want to see if you are passionate about what they are building. Their PPT (Pre Placement Talk) was also focussed majorly on the technologies they are building.
* If you take a question in a direction, make sure you are very very thorough with it. I took it in the direction of compilers, but couldn't make the transition seamlessly because I wasn't thorough with a lot of things (like token generation, visitor invocation).
* Not sure if telling upfront that you don't know about web technologies when you are applying for a profile that might need it is a good idea or not.


Round: Technical Interview
Experience: I think he was a senior person and spoke very passionately about the work that is happening in visa Bangalore office.

Question 1 : I said maybe I should have learnt a little about web based technologies. I think he was looking for a more generic answer.
Question 2 : I went ahead with calculating the expected score where my score random variable = 1 with probability p, and 0 with probability (1-p). I conditioned that expected score of game1 > game2 which would give me the range of p. I goofed up the equations twice but he said he liked my approach and I was just there

Question 3 : I suggested building a graph where a node is a word and an edge means a transition, and then performing BFS. He said that was obvious and that he was more interested in knowing how I build the graph. I suggested a method to reduce the number of string comparisons by storing a count vector with each word. Count vector is a 26 length vector where count[i] = number of times that letter occurs in the word. I would do string comparison to identify neighbours only if the difference in count vectors in 2. Eg, cot = cat - a + o. String comparison is still needed because of false positives. Eg, oct = cat - a + o but cat -> oct is not a valid transition. He liked my approach and asked me to code, discussed the complexity.
Tips: * Don't be naive around a senior engineer. Be confident.
* Explain your approach before going ahead solving it. I missed that in Q1 and for a long time he didn't know what I was heading towards.
* Write clean code, practice coding on paper to make sure you write compilable code. Shabby code is a turn off.
* Show passion for the company you are applying for.

General Tips: * Be friendly and keep smiling.
* Know about the company, well in detail. Recent news, articles, acquisitions, organisational changes, new offices, new product, etc.
* Know about the volume the company handles, certain mind boggling figures, what the company *does not* do
* If you are introducing yourself as an expert in a certain field, be prepared for questions like "How will you contribute to our company with your expertise" type of questions.
* Be very very thorough with every single thing you write on your resume. A small point you weren't sure about might become the basis of your whole interview. Don't write things you are unsure of, or have worked very little on.
Skill Tips: * I think I didn’t take Visa very seriously. I was assuming they won’t take a undergrad and they won’t take me because I have 0 knowledge in web based technologies. I might have acted a little cocky.
* They had nice pie diagrams which shows that they had done thorough research about each and every candidate based on resume and the coding test.
* They value the coding test a lot.
* Be very thorough with the projects you write on resume. They will give you a problem which won't be straightforward and will map onto one of your course projects. You are expected to do the mapping seamlessly. Every bit of the discussion you have with the interviewer can be your next problem.
* Brush up on web based technologies if you can.
* There will be a HR round as well if you clear the technical interviews.

Skills: Maths(esp Probability), Design, Passion, Web Technologies, Technical Skill And Speaking Skill, Coding Skills
College Name: IIT Madras
Motivation: * Been the leader since more than half a century, been through the technological revolution.
* Revolutionising payments architecture. Building something of greatest need, so elegant and optimised, yet producing such consistent performance.
* Keeping up with the need of the generation by introducing features which are brand new. Eg, “all-purpose credit card”.
* Loved their PPT (Pre Placement Talk). Volume of the data and processing is IMMENSE. Billions of transactions in a year voluming up to trillions. More than 200 countries in the world --> these stats are HUGE.
* Fraud detection is a space I would have loved to work on given that I come from a Data Mining background.

Funny Moments: Chucked out before HR round :P

Round: Test
Experience: Coding Questions were fairly standard ones.
Duration: 75 minutes
Total Questions: 42

Round: Interview
Experience: Networks based questions, firewalls, TCP/IP and other OSI layers

Round: Interview
Experience: Coding questions. Asked to code on paper. Questions on Object Oriented Design.

Skills: Networks basics, OOPs basics, Coding Skills
College Name: IIT Guwahati
Motivation: Profiles offered, Package, Location

Round: Test
Experience: Questions on
1. Programming: 10 Questions2. Machine Learning Hadoop MCQ: 6 Questions3. Networking MCQ: 6 Questions4. Operating System: 6 Questions5. Infrastructure: 6 Questions6. Application Security: 6 Questions
Tips: Questions were simple , except sections 2,5 unless you have a basic idea about it.
Duration: 75 minutes
Total Questions: 34+2

Round: Technical Interview
Experience: – Projects, Internship– Asymmetric and Symmetric encryption with some real world usage– Concepts behind Digital Signature and Digital Certificates– Detailed discussion on HTTPS– Basic OS concepts : Threads, Mutex , Semaphores– Basic OOPS concepts : Virtual functions , Function overloading and overriding , encapsulation.
Tips: Focus on Network Security concepts !

Round: Technical Interview
Experience: – Projects , Internship– Some discussion on Testing and how you would design a unit test case and a complete project test case. Discussion on Automated Testing.– How does a Web application work.– Software Development Models– Discussion on interpreted language and compiled language– Some DBMS basics for efficiency :- Indexing viz. B+trees , Hashing.– Some discussion on Apple Pay , VbV (Verified by Visa) (informal)

Round: HR Interview
Experience: Basic HR questions !

General Tips: Confidence is the key along with sufficient coding practice both on the IDE and pen-paper.
Skills: Network Security, Programming, Algorithms, Operating System
College Name: IIT ROORKEE

Round: Test
Experience: 4 Coding questions on Hackerrank platform, one and half hour time. I am not going to reveal the questions here, but one was a basic binary tree implementation and the other three were algorithmic and mathematical problems. They were kinda hard to solve in an hour and half. I could do only 1 and half of the other one. I got 115/300 points on that. I was one of the 16 people selected for the interview.
Tips: It all depends on how well you can focus on the test day. Just practice a lot on hackerrank.
Duration: 1 hour 30 minutes
Total Questions: 4

Round: Technical Interview
Experience: The first two questions I was able to do fast enough. I was also asked a few questions on my resume and coding-related internship. The last one, I showed an O(n*n) algorithm first and then modified it to O(n). Around 45 minutes.
Tips: Be thorough on the coding part in your resume. Think out aloud!

Round: Technical + HR Interview
Experience: Just a few normal questions regarding my projects and my favorite course and it's application to Visa. 15 minutes.
Tips: Once again, be thorough on your resume.

Round: HR Interview
Experience: Once again a normal round, just random questions as to whether I am interested and good enough in communication. 15 minutes.
Tips: Don't get shaken. Be ready for all kinds of questions. Especially about Visa relation to what you do

Skills: Smart Coding
College Name: IIT Madras

Eligibility criteriaAbove 7 CGPAVisa interview preparation:Topics to prepare for the interview - Java, AJAX, Web Development, Node js, DSA, OOPSTime required to prepare for the interview - 5 monthsInterview preparation tips for other job seekers

Tip 1 : Must do Previously asked Interview as well as Online Test Questions.
Tip 2 : Go through all the previous interview experiences from Codestudio and Leetcode.
Tip 3 : Do at-least 2 good projects and you must know every bit of them.

Application resume tips for other job seekers

Tip 1 : Have at-least 2 good projects explained in short with all important points covered.
Tip 2 : Every skill must be mentioned.
Tip 3 : Focus on skills, projects and experiences more.

Final outcome of the interviewSelected