StoreKing Front end Developer Interview Questions and Answers

Q1. What is denbouncer and throttle
Ans. 
Debouncer and throttle are techniques used to limit the frequency of function calls.
• Debouncing delays the execution of a function until a certain amount of time has passed without the function being called again.

• Throttling limits the frequency of function calls to a certain rate, executing the function at fixed intervals.

• Debouncing is useful for events that may be triggered multiple times in quick succession, such as r...read more
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Q2. What is curry function
Ans. 
Currying is a technique of transforming a function that takes multiple arguments into a sequence of functions that each take a single argument.
• Currying allows partial application of a function

• It helps in creating reusable functions

• Curried functions are easier to compose and chain

• Example: const add = (a) => (b) => a + b; add(2)(3) returns 5
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Q3. Implement curry function
Ans. 
Curry function is a higher-order function that allows partial application of arguments.
• Currying transforms a function that takes multiple arguments into a series of functions that take one argument each.

• It returns a new function until all the arguments are received and then executes the original function.

• Example: const add = (a, b) => a + b; const curriedAdd = curry(add); curriedAdd(2)(3) returns 5.
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Q4. What is promise.all()
Ans. 
promise.all() is a method that takes an array of promises and returns a new promise that resolves when all promises in the array have resolved.
• It is used to handle multiple asynchronous operations simultaneously.

• If any of the promises in the array rejects, the returned promise will be rejected with the reason of the first rejected promise.

• The resolved values of the promises are returned as an array in the same order as
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Q5. What is memoization?
Ans. 
Memoization is a technique of caching the results of a function to improve performance.
• Memoization is used to avoid redundant calculations by storing the results of a function and returning the cached result when the same inputs occur again.

• It is commonly used in recursive functions and functions with expensive computations.

• Memoization can be implemented manually or by using libraries like Lodash or Memoizee.

• Example: M...read more
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Q6. What is closure in javascript
Ans. 
Closure is a function that has access to its parent scope even after the parent function has returned.
• Closure allows for private variables and functions in JavaScript.

• It is created when a function returns another function.

• The inner function has access to the outer function's variables and parameters.

• Example: function outer() { let x = 10; return function inner() { console.log(x); } }

• The inner function can access and mo...read more
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Q7. What is the problem with colosures
Ans. 
Closures can cause memory leaks if not handled properly.
• Closures can hold references to variables outside of their scope, preventing them from being garbage collected.

• If closures are used excessively or not released properly, they can cause memory leaks.

• To avoid memory leaks, make sure to release closures when they are no longer needed.
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Q8. Some output questions on SetTimeout to check closure knowledge
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Q9. React lifecycle events
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Q10. Major difference between class based components and class based components
Ans. 
There is no difference between class based components and class based components.
• There seems to be a typo in the question.

• Assuming the question is about functional components vs class components, the major difference is that class components use a class to define the component while functional components are defined as functions.

• Class components have access to lifecycle methods while functional components do not.

• Functi...read more
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Q11. Shallow copy vs deep copy
Ans. 
Shallow copy only copies the reference to an object while deep copy creates a new object with a new memory address.
• Shallow copy is faster and uses less memory than deep copy.

• In shallow copy, changes made to the original object will reflect in the copied object as well.

• Deep copy creates a completely new object with its own memory space.

• In JavaScript, arrays and objects are assigned by reference, so a shallow copy will o...read more
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Q12. How to do deep copy ?
Ans. 
Deep copy creates a new object with the same values as the original object.
• Use Object.assign() method to create a deep copy of an object.

• For nested objects, use recursion to copy all levels.

• For arrays, use slice() method to create a new array with the same values.

• Avoid using spread operator for deep copy as it only creates a shallow copy.
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Q13. What is hoisting? Some questions on it
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Question are very tough and faad

Question like trees linked list and graphs

Q1. Stock buy and sell with at most 2 transaction
Ans. 
Implement a solution to find the maximum profit from buying and selling stocks with at most 2 transactions.
• Use dynamic programming to keep track of maximum profit at each day with 0, 1, or 2 transactions.

• Consider the possibility of splitting the transactions into two separate parts.

• Calculate the maximum profit by iterating through the prices array and updating the maximum profit accordingly.
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Q2. Binary search to find target
Ans. 
Binary search is a divide and conquer algorithm that efficiently finds a target value in a sorted array.
• Divide the array in half and compare the target value with the middle element

• If the target is less than the middle element, search the left half. If greater, search the right half

• Repeat the process until the target is found or the subarray is empty
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Q1. General about project
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Q2. Design paytm wallet
Ans. 
Design a digital wallet system similar to Paytm.
• Allow users to add money to their wallet using various payment methods like credit/debit cards, net banking, UPI, etc.

• Enable users to make payments for various services like mobile recharge, bill payments, online shopping, etc.

• Implement security measures like two-factor authentication, encryption of sensitive data, and regular security audits.

• Provide features like transac...read more
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Q1. What is thread ?
Ans. 
A thread is a lightweight process that can run concurrently with other threads within the same process.
• Threads allow for parallel execution of tasks within a single process.

• Threads share the same memory space and resources of the process they belong to.

• Threads can communicate with each other through shared memory or message passing.

• Examples: Java threads, POSIX threads (pthreads) in C/C++.
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Q2. Inter process communication and project?
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The exam duration is one and a half hours.

The total exam time is one and a half hours.

It encompasses all topics related to full stack development.

Q1. Asks questions on SQL
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Q2. Asks question in typical topics
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Q1. Where do you see yourself in two years?
Ans. 
In two years, I see myself as a senior software developer leading a team on innovative projects.
• Advancing to a senior software developer role

• Leading a team on new and innovative projects

• Continuing to enhance my technical skills through ongoing learning and training
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It was a coding round where i need to solve 3 DSA Questions in 1.5 hour

Q1. This is Technical round where i was asked to implement the Two Question of Dsa one is bases on greedy and another is dp , another one is leetcode hard (finding maxaimal area of rectangle in matrix of 1 and...read more
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Q2. Greedy Q was direct i don't remember clearly. I was selected for the 2nd round
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Q1. It was also a technical round but bases on LLD problem statement. I was given a problem statement to design a society security system and the they need psudo code for complete implementation using correct ...read more
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Q1. I was not selected for 4th round but heard that there were Q on cs fundamentals.
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Q1. The question was about Nodejs
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Q2. The question was to build a linked list in Nodejs
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Q1. The first question was related to DSA
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Q2. The question was related to SQL
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Round duration - 60 Minutes
Round difficulty - Medium

It has 3 Coding Questions of medium-hard level and the time limit was 1 hour only. I don’t exactly remember the questions but I was able to do only two of them completely.

Q1. 
Biggest Number Formation Problem
Your task is to construct the largest number possible by concatenating each of the provided positive integers in the array exactly once.
Input:
Integer T denoting the nu...read more
Ans. 
Construct the largest number by concatenating positive integers in the array exactly once.
• Sort the array of integers in a way that the concatenation of the numbers forms the largest possible number.

• Use a custom comparator function to sort the numbers based on their concatenated values.

• Join the sorted array elements to form the final largest number.
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Q2. 
Number of Longest Increasing Subsequence Problem Statement
Given an integer array ARR of length N, determine the count of longest increasing subsequences present in the array.
Explanation:
The Longest I...read more
Ans. 
Count the number of longest increasing subsequences in an integer array.
• Identify the longest increasing subsequences in the array

• Count the number of such subsequences

• Consider the constraints while implementing the solution

• Examples: For input [50, 3, 90, 60, 80], the output is 2
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Round duration - 60 Minutes
Round difficulty - Medium

First, the interviewer introduced himself and then asked to introduce myself. Then he asked about the projects I did. After an introductory discussion on projects, he gave me 3 coding questions on their personal live code environment.

He asked me to explain the approach first and then code it down. I had to explain the time complexity of each solution and optimal code if possible with lesser time complexity.

Q1. 
Cache Operations Problem
You are provided with a cache that can hold a maximum of 'N' elements. Initially, this cache is empty. There are two main operations you can perform on this cache:
Explanation:
...read more
Ans. 
Implement a cache with insert, update, and retrieve operations, returning results of retrieve operations in order.
• Create a cache data structure with specified size 'N'.

• Implement insert and update operations based on the given criteria.

• For retrieve operation, return the value associated with the 'U_ID' if present, else return -1.

• Handle cases where the cache is full and least frequently used items need to be removed.

• Retu...read more
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Q2. 
Possible Words from a Phone Number: Problem Statement
Given a string S composed of digits ranging from 2 to 9, determine all possible strings that can be created by mapping these digits to their correspon...read more
Ans. 
Given a phone number, generate all possible words by mapping digits to letters on a T9 keypad.
• Create a mapping of digits to letters on a T9 keypad

• Use recursion to generate all possible combinations of letters for the given phone number

• Sort the resulting strings in lexicographical order
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Q3. 
Shortest Unique Prefix Problem
You are given an array containing N words. Your task is to derive the shortest prefix for each word that uniquely identifies it amongst the other words. For instance, given t...read more
Ans. 
Given an array of words, find the shortest unique prefix for each word.
• Create a Trie data structure to efficiently store and search for prefixes.

• Traverse the Trie to find the shortest unique prefix for each word.

• Return the list of shortest unique prefixes for all words.
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Round duration - 60 Minutes
Round difficulty - Hard

In this round interviewer gave me 2 coding questions and asked me to code on any editor of my choice. I opened VS code to code those problems.

Q1. 
Maximum Subarray Sum Problem Statement
Given an array arr of length N consisting of integers, find the sum of the subarray (including empty subarray) with the maximum sum among all subarrays.
Explanation...read more
Ans. 
Find the sum of the subarray with the maximum sum among all subarrays in a given array.
• Iterate through the array and keep track of the maximum sum subarray seen so far.

• Use Kadane's algorithm to efficiently find the maximum subarray sum.

• Handle cases where all elements are negative by returning the maximum element in the array.

• Consider the sum of an empty subarray as 0.
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Q2. 
LRU Cache Implementation
Design and implement a data structure for the Least Recently Used (LRU) cache, which supports the following operations:
1. get(key) - Return the value associated with the key if ...read more
Ans. 
Implement a Least Recently Used (LRU) cache data structure with get and put operations.
• Use a combination of a hashmap and a doubly linked list to efficiently implement the LRU cache.

• Keep track of the least recently used item and remove it when the cache reaches its capacity.

• Update the position of an item in the cache whenever it is accessed or updated.

• Ensure constant time complexity for both get and put operations by u...read more
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Round duration - 40 Minutes
Round difficulty - Easy

The interviewer was very friendly. He asked me about myself and previous interviews.