10+ Mern Stack Developer Interview Questions and Answers for Freshers

Given the head node of a singly linked list, return a pointer to the middle node. If there are an odd number of elements, return the middle element. If there are even elements, return the one farther from the head node.

• Traverse the linked list using two pointers, one moving one node at a time and the other moving two nodes at a time.

• When the fast pointer reaches the end of the list, the slow pointer will be at the middle node.

• If the number of elements is even, return the seco...read more

The task is to find the Huffman codes for each alphabet in an encoded message based on their frequencies.

• The Huffman code is a binary string that uniquely represents each character in the message.

• The total number of bits used to represent the message should be minimized.

• If there are multiple valid Huffman codes, any of them can be printed.

• The input consists of multiple test cases, each with an array of frequencies.

• Implement the function to find the Huffman codes and return 1 ...read more

The question asks to find the total amount of rainwater that can be trapped in the given elevation map.

• Iterate through the array and find the maximum height on the left and right of each bar.

• Calculate the amount of water that can be trapped at each bar by subtracting its height from the minimum of the maximum heights on the left and right.

• Sum up the amount of water trapped at each bar to get the total amount of rainwater trapped.

The task is to find the minimum number of edges that need to be reversed in a directed graph to find the path from a start node to an end node.

• The problem can be solved using graph traversal algorithms like Breadth First Search (BFS) or Depth First Search (DFS).

• Start by creating an adjacency list representation of the directed graph.

• Perform a BFS or DFS from the start node to the end node, keeping track of the number of edges reversed.

• Return the minimum number of edges revers...read more

Rearrange an unsorted array by moving all zeroes to the end while maintaining the order of non-zero elements.

• Iterate through the array and keep track of the count of non-zero elements encountered.

• While iterating, if the current element is non-zero, swap it with the element at the count index.

• After iterating, fill the remaining elements with zeroes.

Find the first repeated character in a given string composed of lowercase English letters.

• Iterate through the string and keep track of characters seen so far in a set.

• If a character is already in the set, return it as the first repeated character.

• If no repeated character is found, return '%'.

The MERN stack consists of MongoDB, Express.js, React.js, and Node.js, enabling full-stack JavaScript development.

• MongoDB: A NoSQL database that stores data in JSON-like documents, allowing for flexible data structures.

• Express.js: A web application framework for Node.js that simplifies server-side development and routing.

• React.js: A front-end library for building user interfaces, allowing for component-based architecture and state management.

• Node.js: A JavaScript runtime that...read more

Java does not support multiple inheritance, but it can be achieved through interfaces.

• Java does not allow multiple inheritance of classes due to the diamond problem.

• However, multiple inheritance can be achieved through interfaces.

• A class can implement multiple interfaces, which can have their own default implementations.

• Example: class A implements Interface1, Interface2 { }

Exception handling is the process of handling errors and unexpected events in a program.

• Exceptions are thrown when an error occurs in the program.

• The try-catch block is used to handle exceptions.

• The catch block catches the exception and handles it appropriately.

• Finally block is used to execute code regardless of whether an exception was thrown or not.

• Exception handling helps in making the program more robust and prevents it from crashing.

Hooks are functions that let you use state and other React features without writing a class.

• useState() - for managing state in functional components

• useEffect() - for side effects in functional components

• useContext() - for accessing context in functional components

• useReducer() - alternative to useState() for more complex state logic

To hash a password, use a secure hashing algorithm like bcrypt.

• Use a secure hashing algorithm like bcrypt to hash the password.

• Generate a salt to add to the password before hashing.

• Hash the password using the bcrypt library function.

• Store the hashed password and the salt securely in the database.

A full stack web app using React

• Set up a Node.js server with Express

• Create a database using MongoDB

• Build the frontend using React components

• Connect frontend to backend using API calls

• Implement user authentication and authorization

• Deploy the app on a hosting platform like Heroku

State and props are two important concepts in React for managing data and passing data between components.

• State is a built-in feature in React components that allows components to have their own internal data that can change over time.

• Props (short for properties) are used to pass data from a parent component to a child component.

• State is mutable and can be changed within the component, while props are read-only and cannot be changed within the component.

• State is typically use...read more

Create a stopwatch using React

• Create a state variable to hold the time

• Use setInterval to update the time every second

• Render the time in the component

• Add buttons to start, stop, and reset the stopwatch

A palindrome is a word, phrase, number, or other sequence of characters that reads the same forward and backward.

• Palindrome is a sequence of characters that reads the same backward as forward

• Examples: 'racecar', 'level', 'deified', 'madam', 'civic'

• Palindrome can also be a phrase or a number, such as 'A man, a plan, a canal, Panama!' or '121'

• Palindrome is commonly used in programming to check if a string is the same when reversed