OLX Senior Android Developer Interview Questions and Answers

Round: Test
Duration: 90 minutes

Skills: Algorithm , OS, DBMS, data structure
College Name: NIT BHOPAL

Round: Test
Experience: Coding questions were comparatively easy. There were three questions.1. Given a string map each character of which to the corresponding digit in a 10 digit mobile phone keypad.2. Don't remember, will add when it comes to my mind.3. Don't remember, will add when it comes to my mind.

Skills: Coding ability, Complete knowledge of working of internet.,
College Name: IIT Bombay

Round: Test
Experience: Just 1 online test



Round - I (90 mins)



Online Test conducted @ HackerRank



a. M.C.Qs (Operating System + Aptitude + C Programming Language + Object Oriented Programming)



b. Programming (2 coding questions)The Online Exam started off after a brief Presentation on Amazon.





The MCQs were largely based on Operating System, Data structures and Algorithms, OOP concepts, C language and Aptitude.



Coding Questions



1. Determine whether a Linked List is a palindrome or not.



2. Given few sets of intervals print out the the entire intervals without overlapping , if they overlap then combine them into one.



Eg: Input : (5,7) (1 , 6) (2 ,4) (10 ,14) (8,9)



Output : (1,7) (8,9) (10,14)



Advice: Must solve at least 1 coding question to have a good chance for selection into the next round
Tips: CGPA holds importance because it is basic eligibility criteria for written test and then secondly it increases odds in your favor of your selection more than those with lower CGPA with same interview performance. Prepare a good resume



1. Prioritize your content



2. Put the most important information first (Academic Projects + Internship)



3. Proofread it twice



Advice : Do your best and leave the rest to god

Round: Test
Experience: Round II

2 Coding questions

1. Classic 2-sum problem

2. Given numbers a, b as the seeds for the Fibonacci sequence determine if a third number 'k' is a part of that sequence or not. (Tricky)
Total Questions: 2

Round: Other Interview
Experience: Round III
1. Tell me about yourself
2. Project + Internship Discussion
3. Compress a given string "aabbbccc" to "a2b3c3"
constraint: inplace compression, no extra space to be used
assumption : output size will not exceed input size

Round: Technical Interview
Experience: Round IV
1. Internship Project Discussion (30 mins)
2. Find the largest count of 0s in a row in a matrix of 0s and 1s sorted in an ascending order row-wise.
3. Replicate a tree with random pointers inplace

Round: Other Interview
Experience: Round V
1. Question related to graphs involving concepts of Depth and Height of a tree. (Took a lot of time in solving it ! but finally recognized the pattern)
2. Maximum size square sub-matrix with all 1s
3. Find the median of an infinite series of integers
4. Find the most popular Google searches. (solved it using Trie and Max-Heaps)
2 more questions but can't remember them.Finally after waiting for more than 9 hours the results were announced and I was selected
Tips: Be cool and always ask the interviewer questions at the end of the interview. Explain the interviewer your progress while solving the question so that you both are on the same page + its easier for him to understand. Behavioral and H.R.
Tips
1. Speak clearly and with confidence
2. Always prepare yourself beforehand for some common questions like:
a. Tell me about yourself.
b. Why should I hire you?
c. What are your strengths and weaknesses? (give examples)
d. What is your Dream Company?

General Tips: They judge you purely on the basis of your knowledge and performance during the face to face interviews. The extra curricular activities are not given much consideration as Amazon focuses its recruitment procedure purely on the basis of your Technical Knowledge. Prepare a good resume
1. Prioritize your content
2. Put the most important information first (Academic Projects + Internship)
3. Proofread it twice
College Name: NIT JAIPUR

Skill Tips: They were looking for really cool coders. High expectation on accurate answers. looking for deep understanding of algorithms and data structures.
Skills: Algorithms, Data structures
College Name: PSIT

Round: Test
Experience: 1 Written Test - (20 MCQ + 2 Coding Questions) on HackerRankAmazon visited our Campus on 28th July. In the morning the recruitment process started with the Written Test. It was taken on Hacker Rank which comprised of 20 MCQ Questions followed by 2 Programming Questions. MCQ Questions usually contain questions on C, DBMS, OS, and 4-5 Logical Questions. One should be aware that the Hacker Rank platform keeps record of how much time you have spent on each Question and after spending so much time did you attempt it or not. The 2 Coding Problems were quite easy. Only speed and accuracy was required to crack this round.Written Round Coding Question -1) A Linked List was given and we had to swap the ith node with (n-i+1)th node.2)(given some intervals), merge the common Intervals.I coded both the problems and passed all the test cases of the first question and half of the test cases of the 2nd Question. By the evening the results of the written round were declared and the Interview Process started. I rushed to the Design Centre and while I was arranging my grade sheets and my resume , something totally unexpected happened. One of the Amazon Employees who was also an Alumni of MNIT Jaipur walked up to me and told me that I have done very well in the Written Test and I was ranked 2nd based on the Written Test. He wished me ‘Best of Luck’ and told me to calm down and give my best. Talking to him really motivated me a lot. At the same time I was shocked that he still remembered my name even after an year, as we had talked only for a couple of minutes during my Internship Process in Amazon in which I was among the last 3 Students who went to the final round but was not selected. Apart from the students shortlisted from the written test, Amazon also shortlists around 5-6 more candidates based on their CGPA and some other factors. But it should be noted that at any time during the Recruitment Process, Cumulative scores can be considered.
Tips: CGPA above 8 should definitely be maintained.
Total Questions: 22

Round: Technical Interview
Experience: The Interview Process started with around 25 candidates. I was among the first few with whom the Interview had started which went on smoothly



Questions of Interview Round II –



1) A String was given with a lot of words in it and I had to reverse all the words
2) A String was given and I have to swap word by word from the  beginning to the end.
3) In question 2 when there are ‘n’ in the String whose position shouldn’t get affected during the swapping process
4) Continuation was when more than 1 ‘n’ occur together.



I was asked to code the above, and told them about the time and space complexities. Then he went through my resume and based on my projects he appreciated my interest in OS. and asked me a Question –


You have a large game and a small memory, so how will you play the game.
I told him the concept of Virtual Memory and how it makes it possible to run such a game. Then he asked me whether there is any limit or constraint on the size of the virtual memory. I explained to him if the amount of memory required at any particular moment of time to run the game, itself exceeds the available size in the RAM for the user, then we won’t be able to play. Then he asked “Suppose you have a 4 GB Ram then how much memory will be available to the user and what will happen to the other memory”. I explained that kernel occupies some memory and apart from that page tables and all are also stored in the memory. Then there were some discussions regarding my projects.
Tips: These is some Important stuff which one should not miss while preparing for the interviews :


Languages one should be knowing for Placements:
1) C : For most of the companies
2) C ++ - For Faster coding using Standard Template Libraries and for OOPS Concept3) Java – For some specific companies which are focused on Java


Operating System:
1) Galvin Text Book
2) Video Lectures by Prof. Kamakoti – IIT Bombay (Not available on NPTEL. You can get it from current student of IIT Bombay or take it from me. I have Video Lectures of 2013 Pass out Batch)
3) Good grasp on OS implementation on Linux and Pint OS.
4) Detail Knowledge of How Threading is implemented in JAVA


Computer Networks:
1) Video Lectures by Prof. Sujoy Ghosh – IIT Kharagpur (Available on NPTEL)
2) Good grasp on Linux Networking (Servers and Networking Commands)


DBMS :
1) SQL Queries.
2) Database Implementation in MY SQL (Using B trees)
3) Indexing and Hashing in DBMS
4) Drawbacks of SQL Database
5) No SQL Database – Graph and Document Type Database and how they solve the problems
6) Every minute detail of the Database you have created in your DBMS Project.


Data Structures and Algorithms:
1) Video Lectures on Data Structures by Prof Naveen Garg – IIT Delhi (Available on NPTEL)
2) Video Lectures on Data Structure and Algorithm by Prof. Charles Leiserson and Prof. Erik Demaine - MIT.
3) TextBook – “Data Structures and Algorithms made Easy” by Karumanchi
4) TextBook – “Cracking the Coding Interview” by Gayle Laakmann Founder and CEO, CareerCup.com
5) GeeksforGeeks6) Company Specific Preparation by Practicing Previous Interview Papers


Programming Practices:
1) Codechef or Any other Coding Website: Experience helps to increase your Programming Speed, definitely useful in qualifying Coding Round
2) Standard Template Library in C++ for faster Coding - Hacker Rank Tutorial


Other Stuff to Study:
1) Brain Teasers
2) Design Problems (asked by Companies like Adobe. Detailed Example in Karumanchi Textbook)
3) Logical And Aptitude Preparation – Arun Sharma TextBook
4) HR Interview preparation from Indiabix.com

Round: Other Interview
Experience: Around 17 students were shortlisted. The resumes of students and their academic projects were given importance while shortlisting for this round. It started at around 10PM.



Questions of Interview Round III –



1) There is a big file containing numbers and we have to sort all of them.



I mentioned the approach mentioned in GeeksforGeeks that for example the available RAM for this purpose is 100 MB. So we can break the File in chunks of 100 Mb and bring the chunks in Memory and first sort them individually. Then we can prepare a heap containing first elements from all chunks. And keep extracting min from heap and replace it by next smallest element of the chunk it belongs. Then he asked if the number of chunks being formed here are very large, that is the heap I am preparing won’t fit in 100MB, then what to do. I suggested some further modifications and finally he was satisfied with the solution.



2) How to implement word suggestions like that in Eclipse.



I explained that it can be done using Tree Data Structure or using some sort of multilevel hashing in combination with storing words in sorted form. He asked me time complexities and told me to think of further improvements. He wasn’t completely satisfied and moved onto the next question.



3) Given 2 integers a and b, the sequence which will be formed is a, b, a+b, a+2b….



i.e Current element = sum of the previous 2 elements.



So now given a number k, how to figure out if it lies in the sequence or not.



This Question is not as easy as it looks. Here a and b can be negative or positive so the Generated Sequence can contain all positive or all negative or alternate occurrence of positive and negative element in sequence. So till which point should we generate the sequence and decide that k can or cannot lie in the sequence. I wrote a code but he mentioned few test cases in which my code was failing. After a few modifications I was able to write a satisfactory code solving all the test cases.

Round: Other Interview
Experience: I answered both the questions and also mentioned  solution to kth largest if Deletion operation is also there and if it is not. Then he told me to write the code for Heapify Function. Again there were some discussion regarding my Projects.

Round: Other Interview
Experience: Questions of Interview Round V -
This round started with a detailed discussion about my Summer Internship Project in Wooqer. After that I was asked to introduce myself. Then he asked me -

1) Given an Infix expression, how to evaluate its answer.

I was asked to write the code for it covering all the cases and I was given half an hour to do it. I wrote it in about 15-20 minutes. Interview of 4th Round got over by about 9 PM, and the results were declared by 11PM.
Tips: Amazon mostly focuses on – Tries, Big Data, Hashing, Strings. Apart from my general preparation for the Interview, I had gone through around 60 Amazon Interview Papers available on GeeksforGeeks, so I was totally aware of the kind of Questions I would be facing in the Interview, and prepared myself accordingly. In this year’s Amazon Interviews mostly the questions asked were not directly from GeeksforGeeks. And few questions which were picked directly from GeeksforGeeks, the solution they were expecting for it was better than that mentioned in GeekforGeeks. But to guess such a solution, one should surely be aware of all the existing solutions in GeeksforGeeks.

General Tips: Self Projects have a very high weight age in one's selection because this is one of the many things that distinguishes you from other candidates sitting in the Interview. It also shows your capabilities and your field of Interest. Also, Summer Internship surely matters a lot in Companies like Amazon. There was a very detail discussion of my Internship at Wooqer during the Interview Process at Amazon so be prepared.
College Name: NIT JAIPUR

Skills:
College Name: NA

Round: Test
Experience: Multiple choice questions pretty much covered everything. This included details of big O notation , concepts from computer organisation etc . Be a little careful while writing outputs as there might be misleading options.
Duration: 90 minutes
Total Questions: 22

Round: Technical Interview
Experience: Building part was quite easy . Should have a little practice of writing code on paper.
Be careful about edge cases . The interviewer took it pretty seriously (things like root node should not be null)

Skills: Data Structures And Algorithms, C and one Object oriented language, Computer Organisation, Basic Aptitude topics like Combinatorics
Duration: 2 months
College Name: IIT Madras