PubMatic Interview Questions and Answers

Basic string manipulation and general DSA questions

Q1. Tree traversal iteratively
Ans. 
Iterative tree traversal uses stacks to explore nodes without recursion, enabling depth-first or breadth-first searches.
• Use a stack for depth-first traversal. Example: Push root, then children.

• For breadth-first traversal, use a queue. Example: Enqueue root, then children.

• In-order traversal: Push left nodes, visit node, then push right nodes.

• Pre-order traversal: Visit node, push left, then right.

• Post-order traversal: Pu...read more
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Q2. Implement DFS,BFS on graph
Ans. 
Implementing Depth-First Search (DFS) and Breadth-First Search (BFS) algorithms for graph traversal.
• DFS explores as far as possible along each branch before backtracking.

• BFS explores all neighbors at the present depth prior to moving on to nodes at the next depth level.

• DFS can be implemented using recursion or a stack; BFS uses a queue.

• Example of DFS: For a graph with edges (A-B, A-C, B-D), starting from A, the order c...read more
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Q1. Java coding for array duplicates
Ans. 
Java code to find duplicates in an array of strings
• Iterate through the array and use a HashSet to keep track of unique elements

• If an element is already in the HashSet, it is a duplicate

• Print or store the duplicates as needed
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Q2. Java code for reverse string without split
Ans. 
Java code to reverse a string without using split method
• Create a char array from the input string

• Use two pointers to swap characters from start and end of the array

• Continue swapping until the pointers meet in the middle
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Q1. Mostly towards your programming and coding ability. 1. Starting from DS, trees, algorithm, multi threading 2. Ask around strings and arrays
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Q2. 1. longest path from node to node in tree
Ans. 
The longest path from one node to another in a tree is the maximum number of edges that must be traversed to reach from one node to another.
• The longest path in a tree is also known as the diameter of the tree.

• The diameter of a tree can be found by first finding the farthest leaf node from any arbitrary node, and then finding the farthest leaf node from that leaf node.

• The sum of the distances from the root to the farthe...read more
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Q1. OS, In death problem solving questions, multi threading.
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Q2. 1. Process 2. Dynamic memory 3. segment corrupted recovery 4. design system to take billions of request
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Q1. Reverse link list
Ans. 
Reversing a linked list involves changing the direction of the pointers between nodes.
• Iterative approach: Use three pointers (prev, current, next) to reverse links.

• Example: For list 1 -> 2 -> 3, after reversal it becomes 3 -> 2 -> 1.

• Recursive approach: Reverse the rest of the list and adjust pointers.

• Example: Base case is when the list is empty or has one node.
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Q2. Count number of digits
Ans. 
Count the number of digits in a given string
• Iterate through each character in the string

• Check if the character is a digit using isdigit() function

• Increment a counter if the character is a digit

• Return the final count of digits
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Q1. What is Apache Kafka?
Ans. 
Apache Kafka is a distributed streaming platform used for building real-time data pipelines and streaming applications.
• Apache Kafka is designed to handle high-throughput, fault-tolerant, and scalable real-time data streams.

• It allows for the publishing and subscribing to streams of records, similar to a message queue.

• Kafka is often used for log aggregation, stream processing, event sourcing, and real-time analytics.

• It p...read more
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Q1. How do you manage stress?
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Q1. Write a code in c c++ or any other language to validate all use cases for an ip address given as input string. Output will be yes or no.
Ans. 
Code to validate all use cases for an IP address input string and output yes or no.
• Use regular expressions to match the input string against the valid IP address pattern.

• Check for valid ranges of each octet (0-255) and proper formatting (4 octets separated by periods).

• Handle edge cases like leading zeros, extra spaces, and invalid characters.

• Return 'yes' if the input string is a valid IP address, otherwise return 'no'.
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Q2. Given 2 sorted integer array print the common value between them. 2 to 3 optimized ways.
Ans. 
Find common values in two sorted integer arrays efficiently.
• Use two pointers approach to iterate through both arrays simultaneously.

• If the current values are equal, add it to the result and move both pointers forward.

• If the current values are not equal, move the pointer of the array with the smaller value forward.
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Q1. What is testing?
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Q2. What are the testing levels?
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Q1. Basic DSA question on array, linked list, graph
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Q2. Loop in kinked list
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Q1. Similar question on DSA and little bit details on previous work experince.
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Q1. Standard managerial round with focus on previous work
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