300+ Interview Questions and Answers

Graph

• Use a graph data structure to represent people as nodes and friend relations as edges

• Each person can be represented as a node with their unique identifier

• Friend relations can be represented as directed edges between nodes

• This allows for efficient traversal and retrieval of friend connections

Custom stack with methods to return min and max elements

• Implement a stack using an array or linked list

• Track the minimum and maximum elements using additional variables

• Update the minimum and maximum variables during push and pop operations

• Implement methods to return the minimum and maximum elements

Given a tree and a node, print all ancestors of Node

• Start from the given node and traverse up the tree

• While traversing, keep track of the parent nodes

• Print the parent nodes as you traverse up until reaching the root

Explanation of useState, useEffect, useMemo, and useCallback hooks in React functional components.

• useState is used to manage state in functional components

• useEffect is used for handling side effects like data fetching, subscriptions, etc.

• useMemo is used for performance optimization by memoizing expensive calculations

• useCallback is used for memoizing functions to prevent unnecessary re-renders

• These hooks enhance functional components by providing state management, side effect ...read more

The for loop will run indefinitely without any condition to terminate it.

• The loop will continue executing until it is manually interrupted or the program crashes.

• This can lead to a program becoming unresponsive or consuming excessive resources.

• It is important to always include a condition in a for loop to control its execution.

To add and manipulate elements in arrays using JavaScript, you can use array methods like splice() and slice().

• Use the splice() method to insert elements into an array at a specific index. For example, arr.splice(index, 0, 'watermelon') will insert 'watermelon' at the specified index without removing any elements.

• To manipulate elements in an array, you can use methods like splice() to remove elements or slice() to extract a portion of the array.

• Remember that arrays in JavaScr...read more

Design and code a scheduler for allocating meeting rooms based on input of room counts and timestamps.

• Create a table with columns for room number, start time, and end time

• Use SQL queries to check for available slots and allocate rooms

• Consider edge cases such as overlapping meetings and room availability

• Use a loop to continuously check for available slots and allocate rooms

• Implement error handling for invalid input

Different approaches for data cleaning include removing duplicates, handling missing values, correcting inconsistent data, and standardizing formats.

• Remove duplicates

• Handle missing values

• Correct inconsistent data

• Standardize formats

• Use statistical methods to identify outliers

• Check for data accuracy and completeness

• Normalize data

• Transform data types

• Apply data validation rules

Hyperparameters of XGBoost, Random Forest, and SVM can be tuned using techniques like grid search, random search, and Bayesian optimization.

• For XGBoost, important hyperparameters to tune include learning rate, maximum depth, and number of estimators.

• For Random Forest, important hyperparameters to tune include number of trees, maximum depth, and minimum samples split.

• For SVM, important hyperparameters to tune include kernel type, regularization parameter, and gamma value.

• Grid ...read more

Code to find median of datapoints in two sorted arrays

• Use binary search to find the median index

• Divide the arrays into two halves based on the median index

• Compare the middle elements of the two halves to determine the median

The problem is to color a graph with two colors such that no two connected vertices have the same color.

• Use a graph coloring algorithm such as Depth First Search (DFS) or Breadth First Search (BFS).

• Start with an arbitrary vertex and color it with one color (e.g., blue).

• Color all its adjacent vertices with the other color (e.g., red).

• Continue this process for all connected components of the graph.

• If at any point, you encounter two adjacent vertices with the same color, it is n...read more

Microservices are implemented using RESTful APIs and message brokers for asynchronous communication.

• RESTful APIs are used for synchronous communication between microservices.

• Message brokers like Kafka or RabbitMQ are used for asynchronous communication.

• Microservices communicate with each other using HTTP requests and responses.

• Each microservice has its own database and communicates with other microservices through APIs.

• Microservices are loosely coupled and can be developed an...read more

Hyperparameters are settings that control the behavior of machine learning algorithms.

• Hyperparameters are set before training the model.

• They control the learning process and affect the model's performance.

• Examples include learning rate, regularization strength, and number of hidden layers.

• Optimizing hyperparameters is important for achieving better model accuracy.

An unique id for a massive parallel system can be generated using a combination of timestamp, machine id and a random number.

• Use a timestamp to ensure uniqueness

• Include a machine id to avoid collisions in a distributed system

• Add a random number to further increase uniqueness

• Consider using a UUID (Universally Unique Identifier) for simplicity

• Ensure the id generation algorithm is thread-safe

Setting up Redux store, connecting components, managing actions and reducers, and using middleware like Redux Thunk or Redux Saga for handling asynchronous actions.

• Setting up a Redux store involves creating a store with createStore() function from Redux, combining reducers with combineReducers(), and applying middleware like Redux Thunk or Redux Saga.

• Connecting components to the Redux store can be done using the connect() function from react-redux library, which allows compon...read more

Data is collected from various sources including databases, APIs, and user input.

• We have access to multiple databases where we can extract relevant data

• We use APIs to gather data from external sources such as social media platforms

• Users can input data through forms or surveys

• We also collect data through web scraping techniques

The sequence of execution of SQL codes is Select-From-Where-Group By-Having-Order By.

• Select: choose the columns to display

• From: specify the table(s) to retrieve data from

• Where: filter the data based on conditions

• Group By: group the data based on a column

• Having: filter the grouped data based on conditions

• Order By: sort the data based on a column

Code to describe database and columns from a table

• Use SQL SELECT statement to retrieve column names and data types

• Use DESC command to get table structure

• Use INFORMATION_SCHEMA.COLUMNS to get detailed information about columns

• Use SHOW CREATE TABLE to get table creation statement

A program to simulate a race with 5 people using multithreading and determine the winner.

• Create a class for the race participants

• Implement the Runnable interface for each participant

• Use a thread pool to manage the threads

• Start all threads simultaneously

• Wait for all threads to finish

• Determine the winner based on the finishing time

Excel functions are pre-built formulas that perform calculations or manipulate data in a spreadsheet.

• Sum: adds up a range of numbers

• Sum if: adds up a range of numbers based on a specified condition

• Count: counts the number of cells in a range that contain numbers

• CountA: counts the number of cells in a range that are not empty

• Count Blanks: counts the number of empty cells in a range

I follow the MVC design pattern as it separates concerns and promotes code reusability.

• MVC separates the application into Model, View, and Controller components.

• Model represents the data and business logic.

• View represents the user interface.

• Controller handles user input and updates the model and view accordingly.

• MVC promotes code reusability and maintainability.

• Example: Ruby on Rails framework follows MVC pattern.

Steps to fit a time series model

• Identify the time series pattern

• Choose a suitable model

• Split data into training and testing sets

• Fit the model to the training data

• Evaluate model performance on testing data

• Refine the model if necessary

• Forecast future values using the model

CSV files are plain text files that store tabular data, while Excel files are binary files that can contain multiple sheets and complex formatting.

• CSV files are simpler and more lightweight compared to Excel files.

• CSV files can be easily opened and edited using a text editor, while Excel files require specific software like Microsoft Excel.

• CSV files do not support formulas, macros, or formatting options like colors and fonts, while Excel files do.

• CSV files have a smaller file...read more

I have handled large amounts of data in my previous roles.

• I have experience handling terabytes of data in my previous role as a data analyst at XYZ company.

• I have worked with data from various sources such as databases, spreadsheets, and APIs.

• I have also used tools like SQL, Python, and Excel to manipulate and analyze data.

• I am comfortable working with both structured and unstructured data.

• I have experience cleaning and transforming data to make it usable for analysis.

We implement multiple checks and balances to ensure payments are credited to the correct employee account.

• We verify the employee's account number and name before processing any payment.

• We implement a two-step verification process to ensure accuracy.

• We conduct regular audits to ensure all payments are correctly credited.

• We have a dedicated team to handle any payment discrepancies or errors.

• We provide training to employees on how to verify and confirm payment details.

• We use adv...read more

Probability of raining given 3 friends with 2/3 truth probability saying it's raining.

• Use Bayes' theorem to calculate the probability

• P(Raining | All Friends Saying It's Raining) = P(All Friends Saying It's Raining | Raining) * P(Raining) / P(All Friends Saying It's Raining)

• P(All Friends Saying It's Raining | Raining) = 1

• P(Raining) = Prior probability of raining

• P(All Friends Saying It's Raining) = Probability of all friends saying it's raining

HAVING is used with GROUP BY to filter the results after grouping. WHERE is used to filter the results before grouping.

• HAVING is used with GROUP BY clause while WHERE is used with SELECT clause.

• HAVING is used to filter the results of aggregate functions while WHERE is used to filter individual rows.

• HAVING is used to filter the results after grouping while WHERE is used to filter the results before grouping.

• HAVING can only be used with aggregate functions while WHERE can be us...read more

Query to find the top five employee salaries

• Use the SELECT statement to retrieve the employee salaries

• Order the results in descending order using the ORDER BY clause

• Limit the results to the top five using the LIMIT clause

Stored procedures are precompiled SQL statements that can be reused and executed multiple times.

• Stored procedures improve performance by reducing network traffic and improving security.

• They can be used to encapsulate business logic and provide a consistent interface to the database.

• Stored procedures can also be used to simplify complex queries and transactions.

• Examples include procedures for inserting, updating, and deleting data, as well as generating reports and performing ...read more

Mocking components in Jest for testing with props and named exports

• Use jest.mock() to mock components and their exports

• For handling props, use jest.fn() to create mock functions and pass them as props to the component being tested

• For named exports, use jest.mock() with a second argument to specify the module's exports

Design a Java-like Garbage Collector with minimal configurations.

• Choose a garbage collection algorithm (e.g. mark-and-sweep, copying, generational)

• Determine the heap size and divide it into regions (e.g. young, old, permanent)

• Implement a root set to keep track of live objects

• Set thresholds for garbage collection (e.g. occupancy, time)

• Implement the garbage collection algorithm and test for memory leaks

I would use a hash table for efficient searching of a lot of data.

• Hash tables provide constant time complexity for search operations.

• They use a hash function to map keys to array indices, allowing for quick retrieval of data.

• Examples of hash table implementations include dictionaries in Python and HashMaps in Java.

Instagram uses a notification system to alert users when they are tagged and displays reels on the profile page based on user preferences and algorithms.

• Instagram uses a push notification system to alert users when they are tagged in a post or story.

• Reels are displayed on the profile page based on user engagement, preferences, and algorithms.

• The Explore page also suggests reels to users based on their interests and interactions on the platform.

Memoization is a technique used in programming to store the results of expensive function calls and return the cached result when the same inputs occur again.

• Memoization helps improve the performance of a function by caching its results.

• It is commonly used in dynamic programming to optimize recursive algorithms.

• Example: Memoizing a Fibonacci function to avoid redundant calculations.

Deadlock is a situation where two or more processes are unable to proceed because each is waiting for the other to release a resource.

• Deadlock occurs when two or more processes are stuck in a circular wait, where each process is waiting for a resource held by another process.

• The four necessary conditions for deadlock are mutual exclusion, hold and wait, no preemption, and circular wait.

• Synchronization refers to the coordination of multiple processes or threads to ensure their...read more

Request flows in Spring Boot MVC, ways to instantiate a bean, and handling Java out-of-memory exception.

• Request flows in Spring Boot MVC: DispatcherServlet receives HTTP request, HandlerMapping maps request to appropriate controller, Controller processes request and returns response.

• Ways to instantiate a bean: Constructor injection, setter injection, and using the @Bean annotation.

• Handling Java out-of-memory exception: Analyze memory usage, increase heap size, optimize code, ...read more

A 5cm wooden cube is cut into smaller 1cm cubes. Determine the number of cubes with different numbers of painted sides.

• The original cube has 125 smaller cubes (5x5x5)

• Each smaller cube has 6 faces, so there are 750 faces in total

• The cubes on the edges have 3 painted sides, the ones on the corners have 3 painted sides, and the rest have 2 painted sides

• There are 8 cubes on the corners, 12 on the edges, and 105 in the middle

• There are 8 cubes with 3 painted sides, 36 with 2 painte...read more

Math.floor() is a method in JavaScript that rounds a number down to the nearest integer.

• Math.floor() returns the largest integer less than or equal to a given number.

• It is commonly used to convert a floating-point number to an integer.

• Example: Math.floor(3.9) returns 3.

A Promise is an object representing the eventual completion or failure of an asynchronous operation.

• A Promise is used to handle asynchronous operations in JavaScript.

• It represents a value that may be available now, or in the future.

• A polyfill for Promise can be implemented using the setTimeout function to simulate asynchronous behavior.

The interviewee was asked about word break, string to integer, and system design for an e-commerce app.

• Word break: Given a string and a dictionary of words, determine if the string can be segmented into a space-separated sequence of dictionary words.

• String to integer: Convert a string to an integer. Handle negative numbers and invalid inputs.

• System design e-commerce app: Design an e-commerce app with features like product listing, search, cart, checkout, payment, and order tr...read more