Watermark Interview Questions and Answers

Round duration - 60 minutes
Round difficulty - Medium

This was a written round. Proper code with correct syntax to be written on paper.
There were 4 questions to be solved in 1 hour. Some questions needed test cases and time complexity to be answered as well.

Q1. 
Add Two Numbers as Linked Lists
You are given two singly linked lists, where each list represents a positive number without any leading zeros.
Your task is to add these two numbers and return the sum as ...read more
Ans. 
Add two numbers represented as linked lists and return the sum as a linked list.
• Traverse both linked lists simultaneously while keeping track of carry from previous sum

• Handle cases where one linked list is longer than the other by padding with zeros

• Create a new linked list to store the sum of the two numbers
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Q2. 
Minimum Number Of Operations To Reach X Problem Statement
Given an array ARR of 'N' integers and an integer 'X', determine the minimum number of operations required to make the sum of removed elements fro...read more
Ans. 
Given an array of integers and a target sum, find the minimum number of operations to make the sum of removed elements equal to the target.
• Iterate from both ends of the array, removing elements until the sum matches the target

• Use a two-pointer approach to efficiently find the minimum number of operations

• If achieving the target sum is not possible, return -1
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Q3. 
Product Of Array Except Self Problem Statement
You are provided with an integer array ARR of size N. You need to return an array PRODUCT such that PRODUCT[i] equals the product of all the elements of ARR ...read more
Ans. 
The problem requires returning an array where each element is the product of all elements in the input array except itself.
• Iterate through the array twice to calculate the product of all elements to the left and right of each element.

• Use two arrays to store the products to the left and right of each element.

• Multiply the corresponding elements from the left and right arrays to get the final product array.

• Handle integer ...read more
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Q4. 
Sort a Stack Problem Statement
You are provided with a stack consisting of 'N' integers. The goal is to sort this stack in descending order by utilizing recursion.
Allowed Stack Operations:
is_empty(S) ...read more
Ans. 
Sort a stack in descending order using recursion without using loop constructs.
• Implement a recursive function to sort the stack in descending order.

• Use the provided stack operations to manipulate the stack.

• Recursively pop elements from the stack, sort them, and push them back in descending order.

• Handle base cases such as an empty stack or a single element stack.

• Ensure the stack is sorted in descending order after the r...read more
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Round duration - 60 minutes
Round difficulty - Easy

General questions based on resume, was asked to explain my internship project.
He asked questions on my written round. Asked me to find the bug in my code for 1st problem. He was extremely happy with me when I gave the correct answer.
He asked me for the code for the last problem since I hadn’t solved it.
Asked to reverse linked list using recursion, since I said I did by iteration earlier.
He had written code of second problem, I had to find bugs in it.
Discussion on quality engineering and developer profiles.

Q1. 
Reverse Linked List Problem Statement
Given a singly linked list of integers, return the head of the reversed linked list.
Example:
Initial linked list: 1 -> 2 -> 3 -> 4 -> NULL
Reversed link...read more
Ans. 
Reverse a singly linked list of integers and return the head of the reversed linked list.
• Iterate through the linked list and reverse the pointers to point to the previous node instead of the next node.

• Use three pointers to keep track of the current, previous, and next nodes while reversing the linked list.

• Update the head of the reversed linked list as the last node encountered during the reversal process.
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Round duration - 60 minutes
Round difficulty - Medium

Technical round that lasted for around 60 minutes. The interviewer asked questions on data structures and OOPS concepts.

Q1. 
Problem: Permutations of a String
Given a string STR consisting of lowercase English letters, your task is to return all permutations of the given string in lexicographically increasing order.
Explanatio...read more
Ans. 
Return all permutations of a given string in lexicographically increasing order.
• Generate all permutations of the given string using backtracking.

• Sort the permutations in lexicographical order.

• Print the sorted permutations separated by space.
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Q2. 
Greatest Common Divisor Problem Statement
You are tasked with finding the greatest common divisor (GCD) of two given numbers 'X' and 'Y'. The GCD is defined as the largest integer that divides both of the...read more
Ans. 
Find the greatest common divisor (GCD) of two given numbers 'X' and 'Y'.
• Implement a function to calculate GCD using Euclidean algorithm

• Iteratively find the remainder of X divided by Y until Y becomes 0

• The last non-zero remainder is the GCD of X and Y
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Q3. What are the differences between C, C++, and Java?
Ans. 
C is a procedural language, C++ is an object-oriented language, and Java is a platform-independent language.
• C is a procedural programming language, while C++ supports both procedural and object-oriented programming.

• C++ is an extension of C with additional features like classes and inheritance.

• Java is a platform-independent language that runs on a virtual machine and uses automatic memory management.

• C is closer to the h...read more
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Q4. What is the purpose of the virtual keyword in C++?
Ans. 
The virtual keyword in C++ is used to declare a member function in a base class that can be overridden in derived classes.
• Virtual functions allow for dynamic polymorphism in C++ by enabling late binding.

• Virtual functions are declared in the base class with the 'virtual' keyword and can be overridden in derived classes.

• When a derived class overrides a virtual function, the function in the derived class is called instead...read more
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Round duration - 60 minutes
Round difficulty - Medium

Technical round that lasted for around 60 minutes. The interviewer asked questions on data structures and question related to cloud computing(cloud computing was listed on my resume) .

Q1. 
LRU Cache Design Question
Design a data structure for a Least Recently Used (LRU) cache that supports the following operations:
1. get(key) - Return the value of the key if it exists in the cache; otherw...read more
Ans. 
Design a Least Recently Used (LRU) cache data structure that supports get and put operations with capacity constraint.
• Implement a doubly linked list to keep track of the order of keys based on their recent usage.

• Use a hashmap to store key-value pairs for quick access and update.

• When capacity is reached, evict the least recently used item before inserting a new item.

• Update the order of keys in the linked list whenever a...read more
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Q2. 
Problem Statement: Delete Node In A Linked List
Given a singly linked list of integers and a reference to a node, your task is to delete that specific node from the linked list. Each node in the linked li...read more
Ans. 
Delete a specific node from a singly linked list given the reference to the node.
• Traverse the linked list to find the node to be deleted.

• Update the pointers to skip over the node to be deleted.

• Print the modified linked list after deletion.
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Round duration - 60 minutes
Round difficulty - Easy

Technical round that lasted for around 60 minutes. The interviewer asked questions on data structures and question related to networking.

Q1. 
Insertion Sort in a Linked List
Given a singly linked list with 'N' nodes containing integer values, your task is to sort the list using insertion sort and output the sorted list.
Insertion Sort is an al...read more
Ans. 
Implement insertion sort algorithm on a singly linked list.
• Traverse the linked list and for each node, find its correct position in the sorted list.

• Keep track of the current node and the previous node to perform the insertion.

• Repeat this process until all nodes are sorted in the linked list.

• Ensure to handle edge cases like empty list or list with only one node.
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Q2. 
Find Duplicates in an Array
Given an array ARR of size 'N', where each integer is in the range from 0 to N - 1, identify all elements that appear more than once.
Return the duplicate elements in any orde...read more
Ans. 
Find duplicates in an array of integers within a specified range.
• Iterate through the array and keep track of the count of each element using a hashmap.

• Return elements with count greater than 1 as duplicates.

• Time complexity can be optimized to O(N) using a set to store duplicates.
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Round duration - 40 minutes
Round difficulty - Easy

The Interviewer asked me questions to know more about me. He also asked a puzzle.

Q1. You have a racetrack with 25 horses. What is the fastest way to determine the top 3 fastest horses, given that you can only race 5 horses at a time?
Ans. 
To determine the top 3 fastest horses out of 25, race horses in groups of 5 and keep track of the fastest horses in each race.
• Divide the 25 horses into 5 groups of 5 horses each.

• Race all 5 horses in each group, keeping track of the top 3 fastest horses in each race.

• After 5 races, you will have the top 3 fastest horses from each group.

• Race the top 3 horses from each group in a final race to determine the overall top 3 f
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