800+ Front end Developer Interview Questions and Answers

The solution checks if an integer array can become non-decreasing by modifying at most one element.

• Iterate through the array and check if there are more than one decreasing pairs of elements.

• If there are more than one decreasing pairs, return false.

• If there is only one decreasing pair, check if modifying one of the elements can make the array non-decreasing.

• If modifying the element at index i-1 or i can make the array non-decreasing, return true.

• Otherwise, return false.

The task is to find the unique number in an array where all other numbers occur twice.

• The array size is given by N = 2M + 1, where M is the number of elements occurring twice.

• Loop through the array and use a hashmap to count the occurrences of each number.

• Return the number with a count of 1, as it is the unique number.

The question is about finding the shortest path distance from a source node to all vertices in an undirected graph.

• The graph is represented by the number of vertices and edges, followed by the edges and their distances.

• The task is to find the shortest path distance from the source node (0) to all other nodes.

• If a node is disconnected from the source node, print the maximum positive integer value (2147483647).

• Implement the function and return the shortest path distances in asc...read more

The task is to encode an N-ary tree into a binary tree and then decode the binary tree back into the original N-ary tree.

• Encode the N-ary tree by representing each node as a binary tree node with its first child as the left child and subsequent children as the right child.

• To decode the binary tree, traverse the binary tree and for each node, create a new N-ary tree node with its left child as the first child and subsequent right children as siblings.

• Use a level order traversa...read more

The task is to check if there exists a path from a given source vertex to a destination vertex in a directed and unweighted graph.

• Read the number of test cases.

• For each test case, read the number of vertices and edges.

• Read the edges of the graph.

• Read the source and destination vertices.

• Implement a graph traversal algorithm (e.g., BFS or DFS) to check if a path exists from the source to the destination.

• Print 'true' if a path exists, otherwise print 'false'.

Sort an array of positive integers (0, 1, 2) in non-decreasing order.

• Use counting sort algorithm to sort the array efficiently.

• Count the occurrences of 0s, 1s, and 2s in the array.

• Update the array with the counts of each element in non-decreasing order.

Use React Router's Redirect component to redirect to login page if user is not logged in.

• Create a PrivateRoute component that checks if user is logged in

• If user is not logged in, redirect to login page using Redirect component

• Wrap the routes that require authentication with PrivateRoute component

The diameter of a binary tree is the length of the longest path between any two end nodes in the tree.

• The diameter of a binary tree can be calculated by finding the maximum of the following three values: 1) the diameter of the left subtree, 2) the diameter of the right subtree, and 3) the longest path that passes through the root node.

• To find the diameter of a binary tree, we can use a recursive approach. We calculate the height of the left and right subtrees, and then calcul...read more

Reverse the order of words in a string without allocating extra space.

• Split the string into words using space as delimiter

• Reverse the order of the words in the array

• Join the words back together with spaces in between

Allocate books to students in a way that minimizes the maximum number of pages assigned to a student.

• Iterate through possible allocations and calculate the maximum pages assigned to a student.

• Find the minimum of these maximums to get the optimal allocation.

• Return the minimum pages allocated in each test case, or -1 if not possible.

Rearrange a linked list such that odd numbers appear before even numbers while preserving the order.

• Create two separate linked lists for odd and even numbers

• Traverse the original list and append nodes to respective odd/even lists

• Combine the odd and even lists while maintaining the order

• Return the rearranged linked list

Use the accept attribute in the input tag to only allow jpg and png files.

• Add accept attribute to input tag with 'image/jpeg, image/png' value

• This will restrict file selection to only jpg and png files

Find the magic index in a sorted array where A[i] = i.

• Iterate through the array and check if A[i] = i for each index i.

• Since the array is sorted, you can optimize the search using binary search.

• Return the index if found, else return -1.

The task is to identify all distinct triplets within an array that sum up to a specified number.

• Iterate through the array and use nested loops to find all possible triplets.

• Check if the sum of the triplet equals the specified number.

• Print the valid triplets or return -1 if no such triplet exists.

Find the most frequent word in a paragraph that is not in a list of banned words.

• Split the paragraph into words and convert them to uppercase for case-insensitivity.

• Count the frequency of each word, excluding banned words.

• Return the word with the highest frequency in uppercase.

Distribute chocolates among students to minimize difference between largest and smallest packets.

• Sort the array of chocolates packets

• Calculate the minimum possible difference between the maximum and minimum number of chocolates in packets distributed to students

• Return the minimum possible difference

Remove duplicates from an array of integers while maintaining order.

• Iterate through the array and add elements to a new array if they are not already present

• Use a hash set to keep track of unique elements

• Return the new array with unique elements in the same order as the original array

Rotate a linked list by K positions in a clockwise direction.

• Traverse the linked list to find the length and the last node.

• Connect the last node to the head to form a circular linked list.

• Find the new head by moving (length - K) steps from the last node.

• Break the circular link and update the head and tail pointers.

• Return the new head of the rotated linked list.

Swap two numbers 'a' and 'b' and output the swapped values.

• Create a temporary variable to store one of the numbers before swapping

• Assign the value of 'a' to 'b' and the temporary variable to 'a'

• Output the swapped values as 'b' followed by 'a'

Given an array of strings, find the lexicographically smallest string that can be used as a prefix to minimize the total cost of deleting prefixes from the strings.

• Iterate through the array to find the common prefix among all strings

• Choose the lexicographically smallest common prefix

• Delete the common prefix from each string in the array to minimize the total cost

Given a sorted alien dictionary in an array of strings, determine the character order of the alien language.

• Iterate through the words in the dictionary to build a graph of character dependencies.

• Perform a topological sort on the graph to determine the character order.

• Return the character array representing the order of characters in the alien language.

Validate if a given string is a palindrome after removing special characters, spaces, and converting to lowercase.

• Remove special characters and spaces from the input string

• Convert the string to lowercase

• Check if the modified string is equal to its reverse to determine if it's a palindrome

Design a Least Recently Used (LRU) cache data structure that supports get and put operations with a given capacity.

• 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 updates.

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

• Update the order of keys in the linked list whenever a key is accessed or updated.

Find the postorder successor of a node in a binary tree.

• Traverse the binary tree in postorder to get the sequence.

• Find the index of the node 'M' in the postorder sequence.

• Return the element at the next index as the postorder successor.

• If 'M' is the last element in the sequence, return -1 as there is no successor.

The return type of getElementsByClassName method in JavaScript is an array of elements.

• The method returns an array of elements that have a specified class name.

• The elements are returned in the order they appear in the document.

• If no elements are found with the specified class name, an empty array is returned.

Find all Jumping Numbers smaller than or equal to a given positive integer N.

• Iterate through numbers from 0 to N and check if each number is a Jumping Number.

• For each number, check if the absolute difference between adjacent digits is 1.

• Include all single-digit numbers as Jumping Numbers.

• Output the list of Jumping Numbers that are smaller than or equal to N.

Calling a function using the new keyword creates a new instance of the function's constructor.

• Creates a new empty object

• Binds 'this' to the new object

• Adds a property to the new object called '__proto__' which points to the constructor function's prototype object

• Returns the new object

Use flexbox to center align a div in just one line in CSS.

• Set the parent container's display property to flex.

• Use the justify-content property with the value 'center' to horizontally center the div.

• Use the align-items property with the value 'center' to vertically center the div.

Check if a given string is a palindrome considering only alphanumeric characters.

• Remove non-alphanumeric characters from the input string.

• Compare the string with its reverse to check for palindrome.

• Handle edge cases like empty string or single character input.

• Use two pointers approach for efficient comparison.

Implement Priority CPU Scheduling algorithm to compute waiting time and turn-around time for processes.

• Implement a function that takes in burst times, priorities, and number of processes as input

• Sort the processes based on priority, with lower process ID as tiebreaker

• Calculate waiting time and turn-around time for each process based on the scheduling algorithm

Javascript is single-threaded.

• Javascript runs on a single thread called the event loop.

• This means that it can only execute one task at a time.

• However, it can delegate tasks to other threads using web workers.

• This allows for parallel processing without blocking the main thread.

Implement a calculator class with chaining methods and delay function.

• Create a Calculator class with add, sub, mul methods that return the instance of the class.

• Implement a delay method that uses setTimeout and returns the instance of the class.

• Use a queue to store the operations and execute them in order after the delay.

• Return the result of the operations when the equals method is called.

Components are building blocks of Angular applications, while directives are used to add behavior to DOM elements.

• Components have a template, styles, and behavior encapsulated together, while directives are used to manipulate the behavior of existing DOM elements.

• Components are typically used to create reusable UI elements, while directives are used to add custom behavior to existing elements.

• Components can have their own view encapsulation, while directives do not have their...read more

You can import all exports of a file as an object in JavaScript using the 'import * as' syntax.

• Use the 'import * as' syntax followed by the object name and 'from' keyword to import all exports of a file as an object.

• For example: import * as myExports from './myFile.js';

• You can then access the exports using dot notation, like myExports.myFunction().

JavaScript data types include string, number, boolean, object, function, undefined, and null.

• String: 'hello'

• Number: 42

• Boolean: true or false

• Object: { key: 'value' }

• Function: function() { }

• Undefined: undefined

• Null: null

Remove duplicate elements from an Array

• Use the Set object to remove duplicate elements

• Convert the Set back to an array using the spread operator

• If the array contains objects, use a custom comparison function

Async/Await is a feature in JavaScript that allows for easier handling of asynchronous code.

• Async/Await is built on top of Promises and provides a more readable and concise way to work with asynchronous code.

• The 'async' keyword is used to define a function as asynchronous, allowing the use of 'await' inside it to pause execution until a Promise is settled.

• Using Async/Await can help avoid callback hell and make code more maintainable and easier to understand.

• Example: async fun...read more

Inheritance is a relationship between a superclass and subclass, while generalization is a relationship between entities with common characteristics.

• Inheritance involves a parent-child relationship where the child class inherits attributes and methods from the parent class.

• Generalization involves grouping entities with common attributes into a higher-level entity.

• Inheritance is a specific form of generalization in object-oriented programming.

• Example: In a database, a 'Car' en...read more

CSS media queries are used to apply different styles based on device characteristics. Min and max define the range of values.

• Media queries allow for responsive design by adapting to different screen sizes and orientations

• Min-width and max-width are commonly used to define the range of screen sizes

• Min-device-width and max-device-width are used to target specific device characteristics

• Other media query features include min-height, max-height, orientation, and resolution

JavaScript is considered a dynamic language because variables can change types based on their current value.

• Variables in JavaScript can hold different types of values at different times

• The type of a variable is determined at runtime, not at compile time

• Dynamic typing allows for flexibility and ease of use in JavaScript programming

• Example: a variable can start as a number and then be reassigned as a string

var is function scoped while let is block scoped in JavaScript.

• var is function scoped, meaning it is accessible throughout the function it is declared in.

• let is block scoped, meaning it is only accessible within the block it is declared in.

• Using var can lead to variable hoisting issues, while let avoids this problem.

• Example: var x = 10; function test() { var x = 20; console.log(x); } test(); // Output: 20

Debounce the API call on input change to optimize performance.

• Implement a debounce function to delay the API call until the user has finished typing.

• Set a time interval for the debounce function to wait before making the API call.

• Cancel the previous API call if a new input change occurs before the time interval is up.

• Use a loading spinner to indicate to the user that the API call is in progress.

• Consider using a caching mechanism to store the API response for future use.

Functional components and class components are not the same in React. Functional components are simpler and more lightweight, while class components have additional features like state and lifecycle methods.

• Functional components are stateless and are just JavaScript functions that return JSX.

• Class components have access to state and lifecycle methods like componentDidMount and componentDidUpdate.

• Functional components are easier to read and test, while class components can be ...read more

jQuery is a fast, small, and feature-rich JavaScript library.

• jQuery simplifies HTML document traversing, event handling, and animating.

• It provides a set of methods for AJAX interactions and DOM manipulation.

• jQuery is cross-platform and supports a wide range of browsers.

• It has a large community and a vast number of plugins available.

• Project architecture depends on the specific project and its requirements.

The process of building a front-end project involves planning, designing, coding, testing, and deploying.

• Gather requirements and create a project plan

• Design the user interface using tools like Figma or Sketch

• Code the front-end using HTML, CSS, and JavaScript

• Test the project for bugs and usability

• Deploy the project to a web server or hosting platform

Develop an app to show all airports in a country on a map and allow users to report incidents after logging in.

• Use a map API like Google Maps or Mapbox to display all airports in the country

• Implement a login system for users to report incidents

• Create a form for users to report incidents with fields like airport name, incident type, and description

• Store incident reports in a database for future reference and analysis

Data can be shared between components in Angular using services, input/output properties, and observables.

• Use services to create a shared data service that can be injected into multiple components

• Use input/output properties to pass data from parent to child components

• Use observables to create a data stream that can be subscribed to by multiple components