WatchGuard Technologies Full Stack Developer Interview Questions and Answers

The task was a Codility type

Round duration - 70 Minutes
Round difficulty - Medium

This was an Online Coding+MCQ round where we had a total of 50 MCQ questions and 1 coding problem. The coding problem was of easy to medium level but was a bit implementation heavy.

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 maintain the order of recently used keys.

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

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

• Update the position of a key in the linked list whenever it is accessed or updated.

• H...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This round had 1 coding question in which I was first required to explain my approach and then discuss the time and space complexities. After this , some basic questions from OOPS and Java were asked.

Q1. 
Detect and Remove Loop in Linked List
For a given singly linked list, identify if a loop exists and remove it, adjusting the linked list in place. Return the modified linked list.
Expected Complexity:
A...read more
Ans. 
Detect and remove loop in a singly linked list in place with O(n) time complexity and O(1) space complexity.
• Use Floyd's Cycle Detection Algorithm to identify the loop in the linked list.

• Once the loop is detected, use two pointers to find the start of the loop.

• Adjust the pointers to remove the loop and return the modified linked list.
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Q2. What is the difference between ArrayList and LinkedList in Java?
Ans. 
ArrayList is implemented using a dynamic array while LinkedList is implemented using a doubly linked list.
• ArrayList provides fast random access but slow insertion and deletion operations.

• LinkedList provides fast insertion and deletion operations but slow random access.

• Example: ArrayList is suitable for scenarios where frequent access and traversal of elements is required, while LinkedList is suitable for scenarios wher...read more
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Q3. What is the difference between abstraction and inheritance?
Ans. 
Abstraction focuses on hiding implementation details, while inheritance allows a class to inherit properties and behavior from another class.
• Abstraction is the concept of hiding the complex implementation details and showing only the necessary features of an object.

• Inheritance is a mechanism where a new class inherits properties and behavior from an existing class.

• Abstraction is achieved through interfaces and abstract...read more
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Round duration - 60 Minutes
Round difficulty - Medium

This round had questions from OS and OOPS. The interviewer also tested my problem solving skills by asking me some puzzles in the end.

Q1. Can you explain piping in Unix/Linux?
Ans. 
Piping in Unix/Linux allows the output of one command to be used as the input for another command.
• Piping is done using the | symbol

• Multiple commands can be piped together

• Piping allows for the creation of complex command chains

• Example: ls -l | grep txt
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Q2. What is a static variable in C?
Ans. 
A static variable in C is a variable that retains its value between function calls.
• Static variables are declared using the 'static' keyword.

• They are initialized only once and retain their value throughout the program's execution.

• Static variables have a default value of 0 if not explicitly initialized.

• They are stored in the data segment of the program's memory.

• Example: static int count = 0; declares a static variable 'c
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Q3. How can you measure exactly 4 liters of water using only a 3-liter can and a 5-liter can?
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Round duration - 60 minutes
Round difficulty - Medium

The test was in the evening which was not too late. It was conducted on Hackerrank which is a very common platform and was hence familiar. There were 26 questions:
Q1: Coding Question
3 languages were allowed: c, java8, python3
Q2 - Q26: Multiple Choice Questions

Q1. 
Intersection of Linked List Problem
You are provided with two singly linked lists containing integers, where both lists converge at some node belonging to a third linked list.
Your task is to determine t...read more
Ans. 
Find the node where two linked lists merge, return -1 if no merging occurs.
• Traverse both lists to find the lengths and the last nodes

• Align the starting points of both lists by moving the longer list's pointer ahead by the difference in lengths

• Traverse both lists simultaneously until a common node is found, which is the merging point
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Basic question asked

Q1. Computer networking based question
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Q2. Dsa question based on graph and dp
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Q3. Based on operating system
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Q4. Function of oops
Ans. 
Object-oriented programming paradigm that focuses on objects and classes for code organization and reusability.
• Encapsulation: bundling data and methods that operate on the data into a single unit (object)

• Inheritance: ability of a class to inherit properties and behavior from another class

• Polymorphism: ability to present the same interface for different data types
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Q1. Behavior question asked
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Round duration - 70 Minutes
Round difficulty - Medium

This was an Online Coding+MCQ round where we had a total of 50 MCQ questions and 1 coding problem. The coding problem was of easy to medium level but was a bit implementation heavy.

Q1. 
Intersection of Linked List Problem
You are provided with two singly linked lists containing integers, where both lists converge at some node belonging to a third linked list.
Your task is to determine t...read more
Ans. 
Find the node where two linked lists merge, return -1 if no merging occurs.
• Traverse both lists to find their lengths and the difference in lengths

• Move the pointer of the longer list by the difference in lengths

• Traverse both lists simultaneously until they meet at the merging point
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Round duration - 60 Minutes
Round difficulty - Medium

The interviewer asked 1 coding problem related to Sliding Window in this round and then the rest of the questions were preety much revolving around Computer Networks and OOPS.

Q1. 
Longest Substring Without Repeating Characters Problem Statement
Given a string S of length L, determine the length of the longest substring that contains no repeating characters.
Example:
Input:
"abac...read more
Ans. 
Find the length of the longest substring without repeating characters in a given string.
• Use a sliding window approach to keep track of the longest substring without repeating characters.

• Use a hashmap to store the index of each character as it appears in the string.

• Update the start index of the window when a repeating character is found.

• Calculate the maximum length of the window as you iterate through the string.

• Return
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Q2. Can you explain what DNS is?
Ans. 
DNS stands for Domain Name System, which translates domain names to IP addresses.
• DNS is like a phone book for the internet, translating human-readable domain names (like google.com) to IP addresses (like 172.217.3.206).

• It helps users access websites by typing in easy-to-remember domain names instead of complex IP addresses.

• DNS servers store records of domain names and their corresponding IP addresses, allowing for effi...read more
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Q3. Explain why MAC addresses are necessary even though we have IP addresses.
Ans. 
MAC addresses are necessary for local network communication and are used to uniquely identify devices on a network.
• MAC addresses are used at the data link layer of the OSI model to identify devices within the same local network.

• IP addresses are used at the network layer to identify devices across different networks.

• MAC addresses are hardcoded into network interface cards (NICs) and are used for communication within the...read more
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Q4. How does C++ support polymorphism?
Ans. 
C++ supports polymorphism through virtual functions and inheritance.
• C++ supports polymorphism through virtual functions and inheritance

• Virtual functions allow a function to be overridden in a derived class

• Base class pointers can point to derived class objects, enabling polymorphic behavior

• Example: class Animal { virtual void makeSound() { cout << 'Animal sound'; } }; class Dog : public Animal { void makeSound() {...read more
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Round duration - 60 minutes
Round difficulty - Medium

This round had questions revolving around Computer Networks and Operating Systems.

Tip : Concepts related to Computer Networks is quite frequently asked in Cisco interviews . So its better to remain equipped with all the fundamental concepts. I prepared all the core subjects from my notes and for revision I would suggest the guided paths of Coding Ninjas , they are very useful for quick revision and also the questions over there are very frequently asked in interviews.

Q1. What is the ARP protocol?
Ans. 
ARP stands for Address Resolution Protocol, used to map IP addresses to MAC addresses in a local network.
• ARP is used to find the MAC address of a device based on its IP address

• It operates at the data link layer of the OSI model

• ARP requests are broadcasted to all devices on the local network

• Example: When a device wants to communicate with another device on the same network, it uses ARP to find the MAC address of the des
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Q2. What are the different types of semaphores?
Ans. 
Different types of semaphores include binary semaphores, counting semaphores, and mutex semaphores.
• Binary semaphores: Can only have two states - 0 or 1. Used for mutual exclusion.

• Counting semaphores: Can have multiple states. Used for synchronization among multiple processes.

• Mutex semaphores: Similar to binary semaphores but with additional features like priority inheritance and deletion safety.
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Q3. What is thrashing in operating systems?
Ans. 
Thrashing in operating systems is a situation where the system is spending more time swapping data between memory and disk than actually executing tasks.
• Occurs when the system is overwhelmed with too many processes competing for limited resources

• Results in a decrease in overall system performance

• Can be alleviated by optimizing memory usage or adding more physical memory

• Example: A system with insufficient RAM running mu
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It was 90 mins test with 2 coding questions and aptitude questions most of them on networking

Q1. Longest subarray with sum 0
Ans. 
Find the longest subarray with sum 0 in an array of integers.
• Use a hash table to store the sum and its index.

• Iterate through the array and calculate the cumulative sum.

• If the cumulative sum is already in the hash table, then the subarray between the current index and the index in the hash table has a sum of 0.

• Keep track of the longest subarray with sum 0 seen so far.

• Return the length of the longest subarray with sum 0.
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Q2. Is a given binary is a binary search tree
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Round duration - 60 Minutes
Round difficulty - Medium

This was an Online Coding+MCQ round where we had a total of 50 MCQ questions and 1 coding problem. The coding problem was of easy to medium level.

Q1. 
Add Two Numbers Represented as Linked Lists
Given two linked lists representing two non-negative integers, where the digits are stored in reverse order (i.e., starting from the least significant digit to ...read more
Ans. 
Add two numbers represented as linked lists in reverse order and return the sum as a linked list.
• Traverse both linked lists simultaneously while keeping track of carry.

• Create a new linked list to store the sum digits.

• Handle cases where one list is longer than the other or there is a final carry.

• Remember to reverse the final linked list before returning the head.
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Round duration - 60 Minutes
Round difficulty - Medium

This round had 1 question related to Binary Tree Traversal and then the rest of the questions that the interviewer asked me were mostly related to OOPS and C++.

Q1. 
Level Order Traversal Problem Statement
Given a binary tree of integers, return the level order traversal of the binary tree.
Input:
The first line contains an integer 'T', representing the number of te...read more
Ans. 
Return the level order traversal of a binary tree given in level order with null nodes represented by -1.
• Create a queue to store nodes for level order traversal

• Start with the root node, enqueue it, then dequeue and print its value, enqueue its children, repeat until queue is empty

• Handle null nodes represented by -1 by skipping them during traversal
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Q2. What is a namespace in C++?
Ans. 
A namespace in C++ is a declarative region that provides a scope for the identifiers within it.
• Namespaces help in organizing code by grouping related classes, functions, and variables.

• They prevent naming conflicts by allowing the same name to be used in different namespaces.

• Example: namespace myNamespace { int x; }

• Example: using namespace std; // for using standard library functions without prefix
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Q3. Why do we need the Friend class and function in Object-Oriented Programming?
Ans. 
Friend class and function in OOP allows specific classes or functions to access private and protected members of a class.
• Friend class/function can access private and protected members of a class without violating encapsulation.

• It allows for selective sharing of data between classes without exposing all members to the outside world.

• Friendship is not mutual - a class can declare another class as a friend, but the other c...read more
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Q4. What does a static member in C++ mean?
Ans. 
A static member in C++ is a member of a class that is shared among all instances of the class.
• Static members are declared using the 'static' keyword.

• They are not associated with any specific instance of the class, but rather with the class itself.

• They can be accessed using the scope resolution operator '::'.

• Static members are commonly used for constants, utility functions, or shared data among all instances of a class.
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Round duration - 60 minutes
Round difficulty - Medium

This round was more aligned towards Computer Networks and had 1 question of DSA realted to Binary Trees and the interview ended with the famous Die-Hard Puzzle.

Q1. 
Spiral Order Traversal of a Binary Tree
Given a binary tree with N nodes, your task is to output the Spiral Order traversal of the binary tree.
Input:
The input consists of a single line containing elem...read more
Ans. 
Implement a function to return the spiral order traversal of a binary tree.
• Traverse the binary tree level by level, alternating the direction of traversal from left to right and right to left.

• Use a queue to keep track of nodes at each level and a stack to reverse the order of nodes at even levels.

• Handle null nodes appropriately to maintain the spiral order traversal.

• Example: For input 1 2 3 -1 -1 4 5, the output should
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Q2. Can you describe the OSI Reference Model?
Ans. 
The OSI Reference Model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven layers.
• The OSI Reference Model stands for Open Systems Interconnection Reference Model.

• It consists of seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.

• Each layer has specific functions and communicates with the adjacent layers.

• The model help...read more
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Q3. What is the use of a router and how does it differ from a gateway?
Ans. 
A router is a networking device that forwards data packets between computer networks. It differs from a gateway in terms of functionality and scope.
• A router operates at the network layer of the OSI model, making decisions based on IP addresses.

• Routers connect multiple networks together and determine the best path for data to travel.

• Gateways, on the other hand, translate between different types of networks or protocols.

• ...read more
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Q4. How can you measure exactly 4 liters of water using only a 3-liter can and a 5-liter can?
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It was Hacker rank test with 5 coding questions

Q1. 2 technical rounds back to back. which involves java, spring boot. 1 DS question
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Q1. HM round around design knowledge check
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