30+ Interview Questions and Answers

Find a missing number in an unsorted array with elements in the range [1,n].

• Use a hash set to store the elements and check for missing numbers.

• Calculate the sum of all elements and subtract it from the sum of the range [1,n].

• Use XOR operation to find the missing number.

The system had over 1 million users worldwide.

• The system had a global user base.

• The user count exceeded 1 million.

• Users were from various countries and regions.

A hashmap is a data structure that stores key-value pairs and allows for constant time lookup and insertion.

• Hashmaps use a hash function to map keys to indices in an array.

• Collisions can occur when multiple keys hash to the same index, which can be resolved using techniques like chaining or open addressing.

• Example: HashMap map = new HashMap<>(); map.put("key", 123); int value = map.get("key");

Implement a simplified Video Codex using data structures

• Use a hash table to store key-value pairs of video frames and their corresponding codecs

• Implement a priority queue to efficiently retrieve the most frequently accessed video frames

• Consider using a linked list to maintain the order of video frames in the codex

Design SkipTracker() for Amazon Prime Music

• SkipTracker() should keep track of skipped songs in Amazon Prime Music

• It should maintain a list of skipped songs as an array of strings

• The list should be updated whenever a song is skipped

• SkipTracker() should provide methods to add, remove, and retrieve skipped songs

Design a chat room system where users can chat with each other and join chat rooms.

• Implement user authentication and authorization to ensure secure access to chat rooms.

• Create a database to store chat messages, user information, and chat room details.

• Develop a real-time messaging system using websockets for instant communication.

• Allow users to create new chat rooms and join existing ones.

• Include features like message history, notifications, and user profiles.

The interview consists of four back-to-back 1 hour sessions with 1 hour lunch break, including system design with the manager and LC medium-hard questions with the rest of the interviewers.

• Prepare for system design questions with the manager by understanding scalability, reliability, and performance considerations.

• Practice solving LC medium-hard questions to showcase problem-solving skills and algorithmic knowledge.

• Take advantage of the lunch break to relax and recharge for t...read more

Designing classes and database for a product

• Identify the entities and relationships in the system

• Create a class diagram with attributes and methods

• Design the database schema with tables and relationships

• Consider performance, scalability, and security

• Use appropriate design patterns and principles

Design a Unix Find File Library

• Implement functions to search for files based on criteria like name, size, permissions, etc.

• Utilize system calls like opendir(), readdir(), and stat() to traverse directories and gather file information.

• Support options for recursive searching, filtering by file type, and specifying search depth.

• Include error handling for cases like permission denied or invalid paths.

• Provide a user-friendly interface with options for displaying results in differe...read more

Design a system to manage deliveries efficiently

• Use a centralized database to store information about deliveries, drivers, and customers

• Implement a tracking system to monitor the status of deliveries in real-time

• Include features like route optimization, delivery scheduling, and notifications for customers

• Consider scalability and reliability to handle a large volume of deliveries

• Integrate with mapping APIs for accurate location tracking

Design a multiplayer game similar to PUBG.

• Create a large map with various terrains and buildings

• Allow players to form teams and communicate with each other

• Include a variety of weapons and equipment for players to find and use

• Implement a shrinking play area to force players into closer combat

• Include a ranking system to encourage competition and skill improvement

High level design for 3 products

• Identify user needs and requirements

• Create a conceptual design for each product

• Define the architecture and components

• Consider scalability, security, and performance

• Document the design and review with stakeholders

Design a system to monitor and alert on system performance and health metrics.

• Define key metrics to monitor such as CPU usage, memory usage, disk space, network traffic

• Implement monitoring agents to collect data from servers and applications

• Set up alerting rules based on thresholds for each metric

• Integrate with notification systems like email, SMS, or Slack for alerts

• Provide a dashboard for visualization of real-time and historical data

Find the maximum area in a histogram.

• Iterate through the histogram and calculate the area for each bar.

• Keep track of the maximum area encountered so far.

• The area of a bar is calculated by multiplying its height with the width (number of consecutive bars) it can extend to.

• Consider using a stack to efficiently calculate the area for each bar.

The Simplify path problem involves simplifying a given absolute path to its canonical form.

• Use a stack to keep track of the directories in the path.

• Split the path by '/' and process each directory.

• Ignore empty directories and '.'.

• If encountering '..', pop the top directory from the stack.

• Join the remaining directories in the stack to form the simplified path.

The question is about solving a problem related to N-ary tree using Depth First Search (DFS).

• Understand the concept of N-ary tree and Depth First Search (DFS)

• Implement the DFS algorithm to traverse the N-ary tree

• Handle the tree nodes and perform necessary operations during traversal

Experiences in system design include designing scalable and efficient software architectures.

• Experience in designing software architectures to meet scalability and performance requirements

• Understanding of system components and their interactions

• Ability to optimize system design for efficiency and maintainability

• Experience with tools and techniques for system design such as UML diagrams and design patterns

Russian doll envelop variant is a problem where you need to find the maximum number of envelopes you can put inside each other.

• Sort the envelopes based on width and height

• Use dynamic programming to find the longest increasing subsequence based on height or width

• The maximum number of envelopes that can fit inside each other is the length of the longest increasing subsequence

Tree traversal problem involves visiting each node in a tree data structure in a specific order.

• There are three main types of tree traversal: in-order, pre-order, and post-order.

• In-order traversal visits the left subtree, then the root, then the right subtree.

• Pre-order traversal visits the root, then the left subtree, then the right subtree.

• Post-order traversal visits the left subtree, then the right subtree, then the root.

Longest common subsequence is the longest sequence of characters that appear in the same order in two or more strings.

• Use dynamic programming to solve this problem efficiently.

• Create a 2D array to store the lengths of longest common subsequences of substrings.

• Traverse the array to find the longest common subsequence.

Design a movie booking system for users to book tickets for movies at various theaters.

• Users can search for movies by title, genre, or theater location.

• Users can select seats and showtimes for the movie they want to watch.

• System should handle payment processing and seat reservations.

• Admins can manage movie listings, theater information, and user bookings.

Design a car cleaning service with various packages and add-on services for customers to choose from.

• Offer different packages such as basic wash, interior cleaning, waxing, etc.

• Provide add-on services like carpet shampooing, leather conditioning, headlight restoration, etc.

• Allow customers to customize their service by selecting specific options they need.

• Implement a loyalty program to reward repeat customers with discounts or free services.

• Consider offering mobile car cleanin...read more

Calculate product of all elements in array except the element itself

• Iterate through array to calculate product of all elements except current element

• Use two arrays to store products of elements to the left and right of current element

• Multiply corresponding elements from left and right arrays to get final product

Word Ladder is a popular problem on LeetCode where you have to find the shortest transformation sequence from start to end word.

• Use BFS to explore all possible transformations from the start word to the end word.

• Build a graph where each word is a node and there is an edge between two words if they differ by one character.

• Keep track of visited words to avoid revisiting them and use a queue for BFS traversal.

• Return the length of the transformation sequence or 0 if no transforma...read more

Gas station problem

• The gas station problem involves finding the minimum starting point from where a circular route can be completed without running out of gas.

• The solution can be obtained using the concept of cumulative sum and tracking the minimum sum encountered.

• If the total sum of gas is greater than or equal to the total sum of cost, a solution exists.

• If there are multiple valid starting points, return the one with the lowest index.

Design Amazon Prime - a subscription service offering fast shipping, streaming of movies, TV shows, music, and more.

• Offer fast shipping for products purchased on Amazon

• Provide access to a library of movies, TV shows, and music for streaming

• Include exclusive deals and discounts for Prime members

• Offer additional services like Prime Video, Prime Music, Prime Reading, and more

The coin change problem involves finding the minimum number of coins needed to make a certain amount of change.

• Start by creating an array to store the minimum number of coins needed for each amount from 0 to the target amount.

• Iterate through each coin denomination and update the minimum number of coins needed for each amount.

• Return the minimum number of coins needed for the target amount.