POPxo Interview Questions and Answers

Round duration - 45 Minutes
Round difficulty - Medium

It was in the mid day and since I applied for a Frontend role the discussion was majorly around data structure and bit of Javascript.
The interviewer was helping and good listener.

Q1. 
Merge Two Sorted Linked Lists Problem Statement
You are provided with two sorted linked lists. Your task is to merge them into a single sorted linked list and return the head of the combined linked list.
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Ans. 
Merge two sorted linked lists into a single sorted linked list without using additional space.
• Create a dummy node to start the merged list

• Compare the values of the two linked lists and add the smaller value to the merged list

• Move the pointer of the merged list and the pointer of the smaller value list

• Continue this process until one of the lists is fully traversed

• Append the remaining elements of the other list to the me
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Q2. 
Sort 0 1 2 Problem Statement
Given an integer array arr of size 'N' containing only 0s, 1s, and 2s, write an algorithm to sort the array.
Input:
The first line contains an integer 'T' representing the n...read more
Ans. 
Sort an array of 0s, 1s, and 2s in linear time complexity.
• Use three pointers to keep track of 0s, 1s, and 2s while traversing the array.

• Swap elements based on the values encountered to sort the array in-place.

• Time complexity should be O(N) and space complexity should be O(1).
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Round duration - 60 Minutes
Round difficulty - Medium

It was more of a in depth round on the framework I'm working on and problem solving.

Q1. What is the event loop and what is its significance?
Ans. 
The event loop is a mechanism in programming that allows for asynchronous execution of code.
• The event loop is a key component in JavaScript's runtime environment, responsible for handling asynchronous operations.

• It continuously checks the call stack for any pending tasks and executes them in a non-blocking manner.

• The event loop ensures that the program remains responsive by allowing other code to run while waiting for ...read more
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Q2. Can you provide examples of output-based questions in JavaScript that utilize browser APIs?
Ans. 
Output-based questions in JavaScript using browser APIs
• Example 1: Write a script that uses the Geolocation API to display the user's current location on a map

• Example 2: Create a program that uses the Web Audio API to play a sound when a button is clicked

• Example 3: Develop a web page that uses the Canvas API to draw a simple animation
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Q3. How would you design a system to support localization in a mobile app?
Ans. 
Designing a system to support localization in a mobile app
• Use resource files to store localized strings for different languages

• Implement a language selection feature for users to choose their preferred language

• Utilize localization libraries or frameworks to streamline the process

• Consider cultural differences when localizing content, such as date formats and currency symbols
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Round duration - 75 Minutes
Round difficulty - Hard

It was more of a fitment/managerial round.
Didn't had any coding questions, but was asked more on approaches and optimisations.
Discussions on the project you have worked on.

Q1. You need to find the fastest 3 horses out of a group, given that you can only race 5 horses at a time. How would you approach this problem?
Ans. 
To find the fastest 3 horses out of a group with 5 horses racing at a time, we can use a tournament style approach.
• Divide the horses into groups of 5 and race them against each other. This will give you the fastest horse in each group.

• Take the winners from each group and race them against each other. The top 3 horses in this final race will be the fastest 3 overall.

• Keep track of the results and compare the timings to d
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Q2. How do you debug the root cause of lag on a screen?
Ans. 
To debug lag on a screen, analyze code, check for memory leaks, optimize rendering, and use profiling tools.
• Analyze code to identify any inefficient algorithms or operations causing lag.

• Check for memory leaks that could be impacting performance.

• Optimize rendering by reducing the number of draw calls, optimizing shaders, and minimizing overdraw.

• Use profiling tools like Xcode Instruments or Android Profiler to identify p
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Q3. Can you explain the architecture of the app you have recently worked on?
Ans. 
The app I recently worked on is a social media platform for sharing photos and connecting with friends.
• The app follows a client-server architecture, with the client being the mobile app and the server handling data storage and processing.

• The client side is built using React Native for cross-platform compatibility.

• The server side is implemented using Node.js with a MongoDB database for storing user data and photos.

• The a...read more
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Round duration - 60 Minutes
Round difficulty - Easy

Q1. 
0/1 Knapsack Problem Statement
A thief is planning to rob a store and can carry a maximum weight of 'W' in his knapsack. The store contains 'N' items where the ith item has a weight of 'wi' and a value of...read more
Ans. 
Yes, the 0/1 Knapsack problem can be solved using dynamic programming with a space complexity of not more than O(W).
• Use a 1D array to store the maximum value that can be stolen for each weight capacity from 0 to W.

• Iterate through each item and update the array based on whether including the item would increase the total value.

• The final value in the array at index W will be the maximum value that can be stolen.
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Q2. 
Find the Second Largest Element
Given an array or list of integers 'ARR', identify the second largest element in 'ARR'.
If a second largest element does not exist, return -1.
Example:
Input:
ARR = [2,...read more
Ans. 
Find the second largest element in an array of integers.
• Iterate through the array to find the largest and second largest elements.

• Handle cases where all elements are identical.

• Return -1 if a second largest element does not exist.
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Round duration - 60 Minutes
Round difficulty - Easy

System Design Round

Q1. Design a system for Twitter, discussing its architecture, key components, and scalability considerations.
Ans. 
Design a scalable system for Twitter with key components and architecture.
• Use microservices architecture for scalability and fault isolation.

• Key components include user service, tweet service, timeline service, and notification service.

• Use a distributed database like Cassandra for storing tweets and user data.

• Implement a message queue like Kafka for handling real-time updates and notifications.

• Use a caching layer like ...read more
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Round duration - 30 Minutes
Round difficulty - Easy

It is just a formality