Amazon React Js Frontend Developer Interview Questions and Answers

Round duration - 60 Minutes
Round difficulty - Medium

This was a Data Structures and Algorithms round with preety good questions . I was expected to come up with an efficient approach and code it as well .

Q1. 
K Closest Points to Origin Problem Statement
Your house is located at the origin (0,0) of a 2-D plane. There are N neighbors living at different points on the plane. Your goal is to visit exactly K neighb...read more
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Q2. 
Power Set Generation
Given a sorted array of 'N' integers, your task is to generate the power set for this array. Each subset of this power set should be individually sorted.
A power set of a set 'ARR' i...read more
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Round duration - 50 Minutes
Round difficulty - Hard

This was also a DSA round where I was asked to code only one of the questions but I eventually ended up coding both as I had some spare time and explained my approches very smoothly to the interviewer . This round went preety well .

Q1. 
Roman Numeral to Integer Conversion
Convert a string representing a Roman numeral into its integer equivalent and return the result.
Explanation:
Roman numerals are represented by seven different symbol...read more
Ans. 
Convert a Roman numeral string to its integer equivalent.
• Create a mapping of Roman numeral symbols to their integer values.

• Iterate through the input string and add the corresponding integer values.

• Handle cases where subtraction is needed (e.g., IV = 4, IX = 9).
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Q2. 
Pair Sum Problem Statement
You are given an integer array 'ARR' of size 'N' and an integer 'S'. Your task is to find and return a list of all pairs of elements where each sum of a pair equals 'S'.
Note:
...read more
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Round duration - 50 Minutes
Round difficulty - Medium

This was also a DSA round with 2 questions . One was implementation heavy and the other was related to recursion and so I handled it carefully so that my code does not run into TLE or Segmentation Fault.

Q1. 
Arithmetic Expression Evaluation Problem Statement
You are provided with a string expression consisting of characters '+', '-', '*', '/', '(', ')' and digits '0' to '9', representing an arithmetic express...read more
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Q2. 
Remove Duplicates from Sorted Array Problem Statement
You are given a sorted integer array ARR of size N. Your task is to remove the duplicates in such a way that each element appears only once. The outpu...read more
Ans. 
Remove duplicates from a sorted array in-place with O(1) extra memory.
• Use two pointers - one for iterating through the array and another for placing unique elements.

• Compare current element with next element to identify duplicates and skip them.

• Update array in-place by moving unique elements to the front.

• Return the length of the array after removal of duplicates.
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Round duration - 50 Minutes
Round difficulty - Medium

This was a typical System Design round where I was asked about the various features of Facebook and what sort of data structures and algorithms are used in implementing them .

Q1. How does Facebook store likes and dislikes?
Ans. 
Facebook stores likes and dislikes using a combination of databases and algorithms.
• Likes and dislikes are stored in databases such as MySQL or Cassandra.

• Algorithms are used to analyze user behavior and recommend content based on likes and dislikes.

• User interactions with posts, pages, and ads are tracked to determine likes and dislikes.

• Likes and dislikes may also be used to personalize the user's feed and target ads mor...read more
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Q2. How does Facebook implement graph search?
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Round duration - 50 Minutes
Round difficulty - Medium

This was a preety intense round as I was grilled more on my System Design concepts but eventually I was able to asnwers all the questions with some help from the interviewer.

Q1. What is Hadoop and why is it used?
Ans. 
Hadoop is a framework for distributed storage and processing of large data sets.
• Hadoop is used for storing and processing big data across a distributed network of computers.

• It is based on the MapReduce programming model, which allows for parallel processing of data.

• Hadoop consists of HDFS for storage and YARN for resource management.

• It is used for tasks like data warehousing, log processing, recommendation systems, and...read more
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Q2. How does Facebook Chat work?
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Round duration - 60 minutes
Round difficulty - Easy

In first round they asked me 2 coding questions where he asked me to code as close as possible to the actual one.

Q1. 
Ninja and Sorted Array Merging Problem
Ninja is tasked with merging two given sorted integer arrays ARR1 and ARR2 of sizes 'M' and 'N', respectively, such that the merged result is a single sorted array w...read more
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Q2. 
Word Distance Calculation
Given a document represented as an array/list ARR of words with length N, find the smallest distance between two given words for multiple queries. The distance is defined as the ...read more
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Round duration - 60 minutes
Round difficulty - Easy

Then in the second round they asked a little about tree and told me to code 2 codes.

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. 
The problem requires implementing a function to return the level order traversal of a binary tree.
• Implement a function that takes the root of the binary tree as input and returns the level order traversal of the tree.

• Use a queue data structure to perform level order traversal.

• Process each level of the tree one by one, starting from the root node.

• Print the node values at each level in the order they appear from left to ...read more
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Q2. 
Combination Sum Problem Statement
Given an array of distinct positive integers ARR and a non-negative integer 'B', find all unique combinations in the array where the sum is equal to 'B'. Numbers can be c...read more
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Round duration - 30 minutes
Round difficulty - Easy

HR round with typical behavioral problems.

Round duration - 60 minutes
Round difficulty - Medium

This was a online test round where I was given 3 DSA questions to be solved in 60 minutes.

Q1. 
Count Ways to Reach the N-th Stair Problem Statement
You are provided with a number of stairs, and initially, you are located at the 0th stair. You need to reach the Nth stair, and you can climb one or tw...read more
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Q2. 
Optimal Strategy for a Coin Game
You are playing a coin game with your friend Ninjax. There are N coins placed in a straight line.
Here are the rules of the game:
1. Each coin has a value associated wit...read more
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Q3. 
Generate All Parentheses Combinations
Given an integer N, your task is to create all possible valid parentheses configurations that are well-formed using N pairs. A sequence of parentheses is considered w...read more
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Round duration - 60 minutes
Round difficulty - Medium

This was a 1 hour online coding round on hackerrank platform. 3 DSA questions were given.

Q1. 
Stock Trading Maximum Profit Problem
Given the stock prices for 'N' days, your goal is to determine the maximum profit that can be achieved. You can buy and sell the stocks any number of times but can onl...read more
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Q2. 
Ninja's Complement Problem Statement
Every day, Ninja dreams of a number but does not understand its significance. Upon investigation, Ninja discovers that converting this number to binary, taking its com...read more
Ans. 
Convert a number to binary, take its complement, and convert back to decimal.
• Convert the given number to binary representation

• Take the complement of the binary number by swapping '1's and '0's

• Convert the complement back to decimal representation

• Return the complement number for each test case
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Q3. 
Bit Majority Number Generation
You are given an array arr consisting of N integers. Construct a number from these integers such that, for each bit position, if the quantity of set bits (1s) is greater tha...read more
Ans. 
Generate a number based on majority set bits in given integers array.
• Iterate through each bit position and count set and unset bits

• Construct the resulting number based on majority set bits at each position

• Return the final constructed number
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Round duration - 60 minutes
Round difficulty - Easy

In this round, a DSA question was first asked. Then a lot of discussion regarding the various test cases around this question took place. (e.g, handing of -ve numbers , decimals , overflow etc).
Main concentration was just to get as many as test cases possible and an efficient solution as well.
And Some common question like why you coding in C++?

Q1. 
Sum of Digits Problem Statement
Given an integer 'N', continue summing its digits until the result is a single-digit number. Your task is to determine the final value of 'N' after applying this operation ...read more
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Q2. What are the advantages of Object-Oriented Programming (OOP)?
Ans. 
OOP allows for code reusability, modularity, and easier maintenance.
• Encapsulation: Bundling data and methods together to protect data from outside interference.

• Inheritance: Allows for the creation of new classes based on existing classes, promoting code reuse.

• Polymorphism: Objects can be treated as instances of their parent class, allowing for flexibility and extensibility.

• Modularity: Breaking down a program into small...read more
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Round duration - 60 minutes
Round difficulty - Easy

Again one coding question to be done on shared screen

Q1. 
Counting Triangles in Graphs
Given two graphs – a directed graph DIR_GRAPH and an undirected graph UNDIR_GRAPH – you are tasked with counting the number of triangles in each of the graphs.
Example:
In t...read more
Ans. 
Count the number of triangles in a directed and undirected graph.
• Parse the input to extract vertices, edges, and edges between vertices.

• Implement a function to count triangles in both directed and undirected graphs.

• Return the counts of triangles for each test case.
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Round duration - 60 minutes
Round difficulty - Easy

Technical Interview round with questions based on DSA, UNIX commands , Web Security etc.

Q1. 
Find The Repeating And Missing Number Problem Statement
You are provided with an array nums which contains the first N positive integers. In this array, one integer appears twice, and one integer is missi...read more
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Q2. What is the difference between the 'ps' and 'top' commands?
Ans. 
ps displays a snapshot of current processes, while top provides real-time information and allows for interactive management.
• ps displays a static list of processes, while top continuously updates the list

• top allows for interactive management of processes (e.g. killing, renicing), while ps does not

• ps is useful for a quick snapshot of processes, while top is useful for monitoring real-time system activity
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Q3. What is cross-site scripting (XSS)?
Ans. 
Cross-site scripting (XSS) is a type of security vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users.
• XSS occurs when a web application allows users to input unvalidated data that is then displayed on the page without proper encoding.

• There are three main types of XSS: stored XSS, reflected XSS, and DOM-based XSS.

• An example of XSS is when a user inputs a script into a sear...read more
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Q4. How can you prevent SQL injection?
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Q5. What is the command to kill all running Java processes?
Ans. 
The command to kill all running Java processes is 'pkill -f java'
• Use the 'pkill' command followed by the '-f' flag and 'java' keyword to kill all Java processes

• Be cautious when using this command as it will terminate all running Java processes

• Make sure to have the necessary permissions to kill processes on the system
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Round duration - 60 minutes
Round difficulty - Medium

Questions based on designing. My first project as it was related to Image processing, so he also asked questions related to it.

Q1. Design a complete system for a traffic enforcement camera.
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Q2. How does JSON (JavaScript Object Notation) work?
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Q3. What software testing frameworks are you familiar with?
Ans. 
I am familiar with testing frameworks such as JUnit, Selenium, and TestNG.
• JUnit

• Selenium

• TestNG
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Q4. What is the best protocol for storing images?
Ans. 
The best protocol for storing images is JPEG (Joint Photographic Experts Group).
• JPEG is a widely used format for storing images due to its high compression ratio and good image quality.

• It supports millions of colors and is compatible with most devices and software.

• Other options include PNG (Portable Network Graphics) for lossless compression and GIF (Graphics Interchange Format) for animations.
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Round duration - 30 minutes
Round difficulty - Easy

This was a typical HR round with questions related to my final year project and some behavioral problems.

Round duration - 60 minutes
Round difficulty - Medium

Technical round with questions based on DSA. Also, there was a discussion on my BTP project.

Q1. 
Longest Palindromic Subsequence Problem Statement
Given a string A consisting of lowercase English letters, determine the length of the longest palindromic subsequence within A.
Explanation:
• A subsequ...read more
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Q2. 
Binary Tree to Doubly Linked List
Transform a given Binary Tree into a Doubly Linked List.
Ensure that the nodes in the Doubly Linked List follow the Inorder Traversal of the Binary Tree.
Input:
The fi...read more
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Q3. 
Palindrome Permutation - Problem Statement
Determine if a permutation of a given string S can form a palindrome.
Example:
Input:
string S = "aab"
Output:
"True"
Explanation:
The permutation "aba" o...read more
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Round duration - 60 minutes
Round difficulty - Medium

Technical interview round where the interviewer asked me questions based on DSA , algorithms and my project. Large set of questions pertaining to DBMS.

Q1. 
Serialize and Deserialize Binary Tree Problem Statement
Given a binary tree of integers, your task is to implement serialization and deserialization methods. You can choose any algorithm for serialization...read more
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Q2. 
Shuffle Two Strings
You are provided with three strings: A, B, and C. Your task is to determine if C is formed by interleaving A and B. A string C is considered an interleaving of A and B if:
• The lengt...read more
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Round duration - 60 minutes
Round difficulty - Medium

This was a design round where I was grilled on my internship , projects and some new design questions were also asked.
Q1. Design a work flow model of the entire work done in your internship.
Q2. Design a workflow model of any one of the projects you did.

Q1. Describe a map-based design for implementing a code that checks for isomorphic words in a file.
Ans. 
Using a map-based design to check for isomorphic words in a file.
• Create a map where the key is the sorted characters of a word and the value is a list of words with the same sorted characters.

• Iterate through the file, for each word, sort its characters and check if it exists in the map. If it does, add the word to the list. If not, create a new entry in the map.

• After processing the file, iterate through the map and out...read more
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Q2. 
Stack with getMin Operation
Create a stack data structure that supports not only the usual push and pop operations but also getMin(), which retrieves the minimum element, all in O(1) time complexity witho...read more
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