PubMatic

PUBMATIC INTERVIEW EXPERIENCE :

Apti:
100% Technical. 

MCQs of OOP, CN, OS, DSA theory and 2/3 coding questions.

⏰ Time: 1 hr 30 mins

Interview: 
Total 3 technical coding Rounds. And 1 HR Call.

1st Interview:
Asked theory questions from all subjects including concepts of CN, OS, OOPs. 1 difficult database query (based on joins) and 2 coding questions. 
⏰ Time: 1 hr 30 mins.

2nd Interview: 
4 coding questions of DSA. 

Array, Circular Queue, Constructors, Tree. 
⏰ Time: 1hr

3rd Interview:
FrontEnd related questions based on Resume.
⏰ Time: 30mins

Tips:

1. Add the coding languages in resume in which you are perfect with.
2. Dont say “No. I don't know” to any question it shows negative impact on interviewer. Give any relatable answer if you dont know the exact answer.
3. Be confident while answering.
4. If interviewer has told to code on any question first tell the basic approach then go for efficiency. And if interviewer is satisfied with your approach then start for coding.
5. For Technical MCQs search on google like top 100 MCQs of CN, Top 100 MCQs of OS and cover every theory subject.
6. Be perfect in any sheet for coding from Array to Trees. If possible cover Heap as well.

All the best!

Aptitude

It consists of two stages:
1. MCQ's

2. Coding questions

 1.MCQ were based on core subjects and OOPS. There were around 30 MCQ questions. Difficulty level of questions were from easy to moderate. Time will be the main constraint for cracking this stage. You have to give correct answers of minimum 75%-80%  MCQs for making your chance to qualify for interview a bit stronger.
2. DSA question were basic, but were application based, there are no straight forward questions as you practice in any of the sheets. You have to use the concept of questions you solved previously in such application based questions. There were three coding questions and you have to solve atleast 2 questions completely and last question must have atleast 50 % test cases passed. Array, string, stack, queue were on main focus.
 

Interview
 

There were total four interview rounds followed my HR call at the end. Total interview rounds depends upon the interviewer, until the interviewer gets satisfied and their requirements are not fulfilled, rounds goes on increasing. But you can expect minimum 3 rounds. First round was consisting of questions based on OS and CN followed by some basic coding questions and OOPS concept. Second round was completly DSA based, I was given four coding questions to solve and was asked to answer some basic OOPS concept simultenously to test multi-tasking. Third consisted of DBMS queries and some resume based stuff, but main focus was on DBMS queries, they check how you can write most efficient query to reduce i/o time. Fourth round again was based on DSA, but here I was given code and was asked to make it time and space efficient. 

Coding questions were based on array, string, stack, queue, tree.(Questions from DSA sheets are enough, just make your basics clear)

Tips:

1. Make sure you are clear with all the concepts of OS, DBMS, CN and OOPS. If not, atleast study sheets that are availalble online that has limited content which can be covered in short time.
2. You must have complete idea of all the things that you mention in your resume, mainly the projets and the tech stacks that you mention.
3. Dont make use of such approaches or technology of which you dont have complete knowlwdge. e.g. I made use of red-black tree during my third round, because I was knowing that the problem given to me can be more efficiently solved by this method. But I was unaware of implementation of red-black tree. You must avoid such things, you can simply say that you dont have any idea.

4. Be confident while giving answers and dont argue with the interviewer. After every round make sure that you ask atleast one question to the interviewer.

5. You must have fully working projects(minimum 2) and must be able to explain the project in proper manner.

6. Make sure you study top interview question from various sites such as interview bit, GFG, tutorials point. It really helps, because interviewer will also be not in touch with core subjects and DSA for years, there are great chances that he will pick the question from these sites.

7. Also study top 50 puzzle question from GFG, most of the interviewer will ask these quiz questions to check your mental ability.

8. Even though if you know the answers of the questions asked by the interviewer, dont suddenly answer the questions, first think then apply some logic then answer.

ALL THE BEST

There were total of 3 rounds.

Round 1: Aptitude
20 MCQs which included SQL, OS,C,C++  and 2 coding questions
1. https://www.geeksforgeeks.org/sum-of-all-possible-expressions-of-a-numeric-string-possible-by-inserting-addition-operators/

2. The Missing Prisoner Prisoners are standing on a Cartesian coordinate system present inside a jail. Each prisoner stands at a unique point with both the coordinates (x,y) being integers. Each prisoner should be at a position that forms a rectangle or square with 3 other prisoners. More formally, every prisoner at a coordinates pair [x, y] should have: at least one prisoner standing at integer coordinates (x. ay) where ay != y. at least one prisoner standing at integer coordinates [bx, y] where bx != x. Unfortunately, one prisoner has escaped. Find the coordinates of that prisoner. Example locations = [[1, 1], [1, 2], (2, 1)] [4. 4), (4, 6], [9. 4). [98]]


Round 2: Interview
 DSA questions 

• - Reverse print Linked list without modifying
• - Print subarray with the largest sum
• Process  vs Thread
  Why performance of thread better than process or vice versa.
• size of class in different conditions like with member function, variables , vptr
  Structure pointers 
  some multithreading questions.
• Some more OS small questions and also pointer questions
  
  Round 3:Interview - Managerial Round
  - Reverse words in a string
  - Binary search 
  - Any search better than binary search ?
  - Do you know working of server ?
• - Implement custom web server in C++ which should handle multiple clients at the same time
• - Implement custom map without any additional external libraries
• - Some Multithreading questions
• - If process p is having pointer to address 1000 can another process pointer p2 access it
  
  
  All the best for your journey up ahead !! If any help needed please connect with me - https://www.linkedin.com/in/abhishek-deokar-006752206/
  
   

1. This content is shared by college pass-out seniors, in case of any help, please contact admin
    

 > Online Assessment (16th july 2022)
 1)visible tower - for ith tower find visible towers at left +right 
   visible are those which having greater height than ith tower, similar to below question
   (https://leetcode.com/problems/number-of-visible-people-in-a-queue/)

 2)Extraordenary substring - a=1,b=1,c=2,d=2,e=2,dialing keypad mapping
  find count of all substring whose sum%len(substring)==0 sum was calculated by mapping

 3) MCQ -15 find output, sql,oops,os,dbms (medium)

 first interview (45-50 min) (18th july 2022)
> introduce yourself
> projects - technology,features,backend,
> coding questions 
   (1) https://leetcode.com/problems/average-of-levels-in-binary-tree/
   (2) https://leetcode.com/problems/missing-number/ (3 appraoches)
> Operating System Questions
  - Memory management
  - what is threading?
  - Deadlock concept
> Questions on oops 
> do you have any questions?

second interview (80-90 min) (19th july 2022)
> introduce yourself
> https://www.geeksforgeeks.org/sorting-larger-file-with-smaller-ram/ 
> based on above question- merge to sorted linked list (https://leetcode.com/problems/merge-two-sorted-lists/)
> Decleare an array to store strings in c
> Malloc and calloc functions
> operating System Questions 
  - paging concept
  -fixed,dynamic partitioning 
> do you have any questions ?

 I had only 2 technical interviews and I was selected,but for some of my friends they took 3-4 interviews
 
 

This content is shared by college passout seniors. In case of any help please contact admin.

Online test : (90 min) MCQs Based on OS , CN , DBMS & 2 coding questions 

Q.1 ) Given specific value for each alphabet from a to z like a-1 , b-1 , c-2, d-2 , e-2 , f-3 ,g-3 ,h-3 , …… , x-9 ,y-9, z-9 Count substrings whose addition of values is perfectly divisible by its length e.g string s = “abcdefg” substring “ab” its value is a+b i.e 1+1 = 2 , 2%2==0 so count is increased 

Q.2 ) One Dynamic programming question on arrays , Height of each tower is given as arr[i] , find number of building visible from each tower 

Technical Interview 1 (65 min)

 1. Tell me about Yourself 

2. Tell me about your projects.. 

3. Which data structure do you know , tell me something about it..? 

4. DSA Q1) given linked list of 0->1->0->1->2->1->0->1 i) count total ones and zeros ii) break this into two linked lists before and after "2" , convert both linked lists into their binary to decimal value 5. DSA Q2) check if given string is valid ip address or not Complete function bool isvalid(char *s){ } 

6. Tell me about different sorting techniques and their time complexities , when and where which one is preferred.. 

7. What are pointers ? What is dereferencing in pointers ? Where pointers are used ? Can we do multiplication or addition of two pointers ? 

8. What's multi threading ? 

9. What is critical section ? What is mutex and semaphore ? 

10. Logical address space vs Physical Address space 

11. What is virtual memory ? What's demand Paging ? What's page fault ? 

Technical Interview 2 (105 min)

 1. Run cpp code in command prompt 

2. Do you know what's Linux ? Have u used it ? 

3. Tell me commands in Linux 4. Given text file with billions of words , count frequency of given words and give output as token Frequency Sort in decreasing order of frequency.. 

5. What are types of map containers in STL ? What's the difference between them ? 

6. Try to solve above's frequency vala problem without stl (he meant to implement our own map for strings ) 

7. What are command line arguments in CPP ? 

8. What's the signature of the main() function in CPP? 

9. Pointers question Given char *str ="welcome" ; char msg[] = "welcome" ; char msg[100] = "welcome"; int a = 3 ; int *ptr = &a ; What will be size of each thing declared over here? 

10. Why pointer is 4 bytes ? Even if your system is 64 bit os..

 11. Why pointer is having 8 bytes size in online compiler ? 

12. What is operator overloading ? 13. Tell me type of constructor in each case string s = token ; string s(token) ; string s 

This interview experience is shared by college pass out senior, In case of any help needed, please contact admin

ROUND 1)- Technical Round
1) Tell me about yourself?
2) What will be the output of the following codes in java?
i) String s1="java";
String s2='java";
sysout(s1==s2 );
sysout(s1.equals(s2));
Ii) String s1="java";
String s2=new String("java");
sysout(s1==s2 );
sysout(s1.equals(s2));
iii) String s1=new String("java");
String s2=new String('java");
sysout(s1==s2 );
sysout(s1.equals(s2));
3) Compare & discuss the following collection frameworks based on the time complexities of different 
operations.
i) ArrayList vs LinkedList
ii) HashSet vs TreeSet.
4) Differentiate comparable and comparator in java.
5) Discuss four pillars of OOPs in java in brief.
6) What is Multithreading? How will you create a thread in java?
7) What are the states of the thread? 
8) What is Deadlock? What are the necessary conditions for it? How will you prevent it?
9) What is Virtual memory & demand Paging?
10) Question: Find minimum jumps to reach at the end of the array? 
(link=https://leetcode.com/problems/jump-game-ii/)
(My approach -> i) Recursive brute force ->T.C.=O(n!) S.C.(extra)=O(n); 
i) Dynamic Programming ->T.C.=O(n*n) S.C.(extra)=O(n); 
i) Greedy Approach(Valley-peek approach) ->T.C.=O(n) S.C.(extra)=O(1);) 
2
ROUND 2)- Technical Round
1. Implement a linked list as a queue, perform insert, delete, and getSize operation in O(1) 
complexity, and write clean & concise code for it using OOPs concepts
2. Find the Peek element from the given array(Hill type array) (https://www.geeksforgeeks.org/finda-peak-in-a-given-array/) (Expected complexity- O(log(n))).

Online Assessment (90 minutes)
Platform: HackerRank

• 15 MCQs on core Computer Science fundamentals
• 2 coding questions based on strings
•  

Shortlisting Criteria

• Shortlist was based on the Online Assessment score and CGPA.
•  

Technical Interview 1

Duration: 1 hour

Started with “Tell me about yourself.”

CS Fundamentals:

OS:

• What is virtual memory?
• Explain the concept of thrashing.
• CPU scheduling algorithms.
• CN:
• Explain how DHCP works.
• DBMS:
• Provided two tables and asked queries based on joins and subqueries.
• OOPS and programming languages :
• Explain the pillars of OOP.
• What is a friend function and its application?
• What is the volatile keyword?
• How to create a thread?
• Exception handling.
• Difference between structure and class.
• What is a dangling pointer, associated issues, and how to handle it?

Project Discussion:
Discussion based on my project work.

Data Structures & Algorithms (DSA):

• Mirror image of a complete binary tree.
• Reverse nodes in k-group (asked to write code and dry run on given test cases).

Final Question:
Do you have any questions for me?
This is an opportunity to show your curiosity and understanding of the company's work. Asking about any terms you came across during company research can be beneficial.

Technical Interview 2

Duration: 1.5 hours

The interviewer went through my resume and explained the structure of the interview:

DSA problem

Project discussion

System Design

SQL queries

DSA Problem:

• Longest Increasing Subsequence: I explained the brute force and memoization approaches. The interviewer asked for a dry run, recursive tree, and DP table.

Project Discussion:

• Explained overall functionality and tech stack.

System Design Problem:

• Shorten URL service: The focus was more on schema, scaling, and database design rather than how the URL is shortened. Discussed schema design, scaling through partitioning, horizontal/vertical scaling, rate limiting. and CAP theorem.

SQL Queries:

• The interviewer drew a tree representing an organizational hierarchy (e.g., manager and employee) and asked multiple queries based on it.

Both interviews were held on the same day, and the results were communicated within a week. At our time, no HR round was conducted.

PubMatic shortlisted students based on CGPA criteria for online test.

26-08-2024 :

Online Assessment (90 minutes) -

Platform: HackerRank

Test includes MCQ's based on OS, DBMS, CN, DSA and two coding questions based on strings.

They shortlisted 10 students for interviews. Interview conducted at PubMatic office, Pune.

29-08-2024:

Technical Interview 1 -

Duration :- 1.5 hours

• How was the journey to pune?
• Project discussion - Asked me to explain the projects.
• Asked me to show how my app works on paper and also asked some questions about frontend and backend.
• My contribution into the project.
• DSA question- given a string and you have to find out min. no of operations to make a string balanced (Asked to explain the approach, write code and dry run on given test cases).
• SQL query - Interviewer drew the Student table which had columns like RollNo, Name, Branch, Marks. He asked me to write down the query to fetch student having maximum marks in CSE department.
• OS - Interviewer asked me about primary and secondary memory.
  Let's say size of RAM is 8GB and you have a movie on hard disk of 5GB. 2GB space in RAM is free and you try to watch the movie. How OS works here. I explained him how OS handles this situation efficiently by making use of virtual memory and also drew the working on paper.

Technical Interview 2 -

Duration :- nearly about 1.5 hours

• Tell me about yourself.
• What is heap memory?
• What are the pointers? - Interviewer asked me deep questions about pointers and their working when we pass pointer as parameter to function. I explained the concept of double pointers and how we can use them to modify the pointer itself inside the function.
• Vector implementation using array - approach and code.
• Vector implementation using pointer array - approach and code.
• String problem - given a string (a sentence containing multiple words) where we have to find the given string (word) and replace it by another given string (word) - approach and code .
• Do you have any questions for me?

No HR was conducted and Results were announced on 2 sep 2024.

Final Verdict : Selected