60+ Facebook Interview Questions and Answers

The task is to find the cheapest price from the given source to destination with up to K stops.

• Read the number of test cases

• For each test case, read the number of stations and trains

• Read the details of each train (source, destination, ticket price)

• Read the source station, destination station, and maximum number of stops

• Implement a graph data structure to represent the stations and trains

• Use a modified version of Dijkstra's algorithm to find the cheapest price with up to K sto...read more

The task is to find the length of the longest increasing path in a 2D matrix, where you can move in four directions: left, right, up, or down from each cell.

• Traverse the matrix and for each cell, find the longest increasing path starting from that cell

• Use dynamic programming to store the length of the longest increasing path for each cell

• Recursively explore all four directions from each cell, checking if the next cell is greater than the current cell

• Keep track of the maximum ...read more

Convert a decimal number to base 58 using a specific alphabet.

• Iterate through each test case and convert the decimal number to base 58 using the given alphabet.

• Handle the conversion by dividing the number by 58 and taking the remainder to find the corresponding base 58 character.

• Build the base 58 representation by appending the characters in reverse order.

• Output the final base 58 representation for each test case.

The task is to construct a binary tree using the given inorder and preorder traversals.

• Use the preorder traversal to determine the root of the binary tree

• Use the inorder traversal to determine the left and right subtrees of the root

• Recursively construct the left and right subtrees

• Return the root node of the constructed binary tree

Given a hashmap M and an input string S, return an array of all possible mutations of S using M's substitutes.

• Iterate through each character in S and get its substitutes from M

• Use recursion to generate all possible combinations of substitutes for each character

• Time complexity: O(n^m) where n is the average number of substitutes per character and m is the length of S

• Space complexity: O(n^m) due to the number of possible combinations

• Optimization: Use memoization to store previo...read more

The task is to find all unique combinations in an array whose sum is equal to a given target sum.

• Use backtracking to generate all possible combinations

• Sort the array in non-decreasing order to ensure elements in each combination are in non-decreasing order

• Start with an empty combination and iterate through the array, adding each element to the combination and recursively calling the function with the remaining sum

• If the sum becomes zero, add the combination to the result

• If th...read more

Function to return list of friends of friends in decreasing order of mutual friends

• Use a set to store all friends of friends

• Iterate through the list of friends of the given id

• For each friend, iterate through their list of friends and count mutual friends

• Sort the set of friends of friends by decreasing number of mutual friends

Given a list of numbers and symbols, provide an expression that evaluates to a target number.

• Use recursion to try all possible combinations of numbers and symbols

• Check for division by zero and negative numbers

• Return False if no expression evaluates to the target number

The task is to merge accounts belonging to the same person based on common emails and return the merged accounts.

• Iterate through each account and create a mapping of emails to account holders

• Iterate through the mapping and merge accounts with common emails

• Sort the merged accounts and return the result

The task is to print every path of a binary tree with the sum of nodes in the path as 'K'.

• Traverse the binary tree and keep track of the current path and its sum

• At each node, check if the sum of the current path equals 'K'

• If yes, add the current path to the result

• Continue traversing the left and right subtrees recursively

• Remove the current node from the path before backtracking

Calculate the total number of distinct paths from a given source node to all other nodes in a directed graph.

• Use dynamic programming to keep track of the number of paths from the source node to each node in the graph.

• Consider using modular arithmetic to handle large numbers and prevent overflow.

• Start by initializing the number of paths from the source node to itself as 1.

• Iterate through the edges of the graph and update the number of paths for each destination node.

• Return the...read more

The task is to find the maximum number of fruits a bird can gather within a given time frame, moving between adjacent trees.

• Start from each tree and calculate the maximum fruits that can be gathered within the time frame.

• Use a sliding window approach to keep track of the fruits collected while moving between trees.

• Choose the starting tree that gives the maximum total fruits collected.

• Example: For input N=7, M=3, ARR={2, 1, 3, 5, 0, 1, 4}, the output is 9 by starting from tree...read more

The task is to find all distinct triplets in an array that sum up to a specified number.

• Iterate through the array and use nested loops to find all possible triplets.

• Use a set to store unique triplets and check if the sum equals the target sum.

• Handle edge cases like duplicate elements and no valid triplets.

• Return the triplets or -1 if no valid triplet exists.

Function to return mutual friends given two ids and getFriends(id) function

• Call getFriends(id) for both ids to get their respective friend lists

• Iterate through both lists and compare to find mutual friends

• Return the list of mutual friends

Count distinct pairs in an array whose sum equals a given target.

• Use two pointers approach to iterate through the array and find pairs with sum equal to target.

• Keep track of visited pairs to avoid counting duplicates.

• Return -1 if no such pair exists with the given target.

Return all prime numbers less than or equal to a given positive integer N.

• Iterate from 2 to N and check if each number is prime using a helper function.

• A number is prime if it has only 2 factors: 1 and itself.

• Optimize by checking divisibility only up to square root of the number.

Find the length of the longest path from a source cell to a destination cell in a binary matrix.

• Use depth-first search (DFS) to explore all possible paths from source to destination.

• Keep track of visited cells to avoid revisiting them.

• Return the length of the longest path found, or -1 if no path exists.

Compute running absolute difference of elements at even and odd index positions in an array.

• Iterate through the array and calculate absolute difference between elements at even and odd indices.

• Keep track of running absolute differences for even and odd indices separately.

• Output the final running absolute differences for even and odd indices.

Given courses with prerequisites, determine a valid order to complete all courses.

• Use topological sorting to find a valid order of courses.

• Create a graph with courses as nodes and prerequisites as edges.

• Start with courses that have no prerequisites and remove them from the graph.

• Continue this process until all courses are taken or there are no valid courses left.

• If there is a cycle in the graph, it is impossible to complete all courses.

Merge overlapping intervals and return sorted list of merged intervals.

• Sort the intervals based on start times.

• Iterate through intervals and merge overlapping intervals.

• Return the merged intervals in sorted order.

Given a rotated sorted array, find the index of a given integer 'K'.

• Use binary search to find the pivot point where the array is rotated.

• Then perform binary search on the appropriate half of the array to find 'K'.

• Handle cases where 'K' is not present in the array by returning -1.

Given an array and an index, find the number of elements smaller than the element at that index appearing before it in the array.

• Iterate through the array up to index K and count the number of elements smaller than ARR[K].

• Return the count as the rank of ARR[K].

• Handle edge cases like empty array or invalid index K.

Design a Least Recently Used (LRU) cache data structure that supports get and put operations with capacity constraint.

• Implement a doubly linked list to maintain the order of recently used keys.

• Use a hashmap to store key-value pairs for quick access.

• Update the order of keys in the linked list on get and put operations.

• Evict the least recently used key when the cache reaches its capacity.

Generate the power set of a sorted array of integers with individually sorted subsets.

• Use recursion to generate all possible subsets by including or excluding each element in the array.

• Sort each subset before adding it to the power set.

• Handle base cases for empty array and single element array.

• Ensure the subsets are unique by using a set data structure.

• Time complexity can be exponential due to the nature of generating all subsets.

Find the K closest points to the origin in a 2-D plane using Euclidean Distance.

• Calculate the Euclidean Distance of each point from the origin

• Sort the points based on their distances

• Return the first K points as the closest neighbors

Given time slots, find a specific time with maximum overlap. Prove solution.

• Create a list of all start and end times

• Sort the list in ascending order

• Iterate through the list and keep track of the number of overlaps at each time

• Return the time with the maximum number of overlaps

• Prove solution by testing with different input sizes and edge cases

Use a min-heap to keep track of the largest K numbers seen so far.

• Create a min-heap of size K.

• For each incoming integer, add it to the heap if it's larger than the smallest element in the heap.

• If the heap size exceeds K, remove the smallest element.

• At the end, the heap will contain the largest K numbers in the input.

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).

Find the length of the longest strictly increasing subsequence in an array of integers.

• Use dynamic programming to solve this problem efficiently.

• Initialize an array to store the length of the longest increasing subsequence ending at each index.

• Iterate through the array and update the length of the longest increasing subsequence for each element.

• Return the maximum value in the array as the result.

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.

Find the longest sub-array with increasing order of integers.

• Iterate through the array and keep track of the current sub-array's start and end indices.

• Update the start index whenever the current element is smaller than the previous element.

• Update the end index whenever the current element is greater than or equal to the next element.

• Calculate the length of the sub-array and compare it with the longest sub-array found so far.

• Return the longest sub-array.

iOS manual memory management requires developers to manually allocate and deallocate memory for objects.

• Developers must manually allocate memory for objects using methods like alloc and init.

• Developers must also manually deallocate memory for objects using methods like release.

• Failure to properly manage memory can lead to memory leaks and crashes.

• ARC (Automatic Reference Counting) was introduced in iOS 5 to automate memory management.

• However, manual memory management is still...read more

Program to print powerset of a given set

• Create an empty list to store subsets

• Loop through all possible binary numbers from 0 to 2^n-1 where n is the length of the set

• For each binary number, convert it to binary and use the 1's as indices to select elements from the set

• Add the selected elements to the list of subsets

• Return the list of subsets

Code to find a given integer in a rotated sorted array.

• Use binary search to find the pivot point where the array is rotated.

• Divide the array into two subarrays and perform binary search on the appropriate subarray.

• Handle edge cases such as the target integer not being present in the array.

Find the length of longest increasing subsequence and print the sequence from an array of integers.

• Use dynamic programming to solve the problem

• Create an array to store the length of longest increasing subsequence ending at each index

• Traverse the array and update the length of longest increasing subsequence for each index

• Print the sequence by backtracking from the index with the maximum length

• Time complexity: O(n^2)

• Example: Input array [3, 4, -1, 0, 6, 2, 3], output length 4 a...read more

Solve for x in a given expression with single variable.

• Simplify the expression by applying the distributive property and combining like terms.

• Isolate the variable term on one side of the equation and the constant terms on the other side.

• Solve for x by dividing both sides of the equation by the coefficient of the variable term.

• Check the solution by substituting the value of x back into the original equation.

• In this case, simplify the expression to -5x/3 = -4 and solve for x to...read more

Facebook stores likes/dislikes using a combination of databases and caching systems.

• Likes/dislikes are stored in a distributed database system like Cassandra or HBase.

• Each like/dislike is associated with a user and the content being liked/disliked.

• The database is sharded to handle the large volume of likes/dislikes.

• Caching systems like Memcached or Redis are used to improve read performance.

• Likes/dislikes can be stored as separate entities or as counters depending on the use ...read more

Facebook implements graph search by indexing user connections and content to enable efficient search queries.

• Facebook indexes user connections and content to build a graph database.

• The graph database is used to store and retrieve information about users, their relationships, and their content.

• Graph search queries are executed by traversing the graph database to find relevant connections and content.

• Facebook uses various algorithms and optimizations to improve the efficiency a...read more

Facebook implements graph search by indexing user data and using natural language processing.

• Facebook indexes user data to create a graph of connections and relationships.

• Natural language processing is used to interpret user queries and return relevant results.

• Graph search allows users to search for specific information within their network, such as 'friends who like hiking'.

Find k closest points to origin from a set of 2D points.

• Calculate distance of each point from origin using distance formula

• Sort the points based on distance in ascending order

• Return first k points from the sorted list

Hadoop is a distributed computing framework used for storing and processing large datasets.

• Hadoop is based on the MapReduce programming model.

• It allows for parallel processing of large datasets across multiple nodes.

• Hadoop consists of two main components: HDFS for storage and MapReduce for processing.

• It is commonly used for big data analytics, machine learning, and data warehousing.

• Examples of companies using Hadoop include Facebook, Yahoo, and eBay.

Facebook Chat is a real-time messaging system that allows users to send and receive instant messages.

• Facebook Chat uses a client-server architecture.

• It utilizes long polling or WebSockets for real-time communication.

• Messages are stored in a message queue for delivery.

• Chat messages are encrypted for security.

• Facebook Chat supports features like read receipts, typing indicators, and group chats.

Convert Roman numerals to integer in O(n) time

• Create a dictionary to map Roman numerals to integers

• Iterate through the string from right to left

• If the current numeral is less than the previous, subtract it from the total

• Else, add it to the total

• Return the total

Status updates can be implemented through various methods such as push notifications, real-time updates, and periodic polling.

• Use push notifications to instantly update users on important changes.

• Implement real-time updates using websockets or server-sent events for a seamless user experience.

• Periodically poll the server for updates using AJAX or other similar technologies.

• Provide a clear and concise interface for users to view and interact with status updates.

• Consider implem...read more

Facebook stores likes/dislikes as data points in their database.

• Likes and dislikes are stored as separate data points.

• Each like/dislike is associated with a unique ID for the post or comment.

• The data is stored in Facebook's database and can be accessed through their API.

• Likes/dislikes can also be used to personalize a user's newsfeed.

• Facebook also uses likes/dislikes to gather data for targeted advertising.

FB messages work by allowing users to send and receive text, images, videos, and other media through the Facebook platform.

• Messages can be sent to individuals or groups of people.

• Users can also send voice messages and make voice and video calls through the messaging feature.

• Messages can be archived or deleted, and users can also choose to ignore or block certain senders.

• Facebook uses end-to-end encryption to protect the privacy and security of messages.

• Messages can be accesse...read more

FB Mail is a messaging service that allows Facebook users to send and receive messages from other users.

• FB Mail is integrated into the Facebook platform and can be accessed through the Messenger app or website.

• Users can send messages to individuals or groups, and can also attach files, photos, and videos.

• FB Mail also includes features such as message requests, message filtering, and message archiving.

• Messages can be sent and received in real-time, and users can also receive n...read more

My favorite product is the iPhone. I would improve it by increasing battery life and adding more customization options.

• Increase battery life

• Add more customization options

• Improve Siri's functionality

• Make the camera even better

• Offer more color options

Demand paging is a memory management technique where pages are loaded into memory only when needed.

• Demand paging allows for efficient memory utilization by loading pages into memory on demand.

• It reduces the amount of initial memory required to start a process.

• When a page is needed but not in memory, a page fault occurs and the required page is loaded from disk.

• Demand paging allows for larger virtual memory space than physical memory.

• Examples of demand paging systems include W...read more

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 more.

• Popular tools in the Hadoop ecosystem include Apache...read more

The responsibility for illegal rules lies with the individuals or entities that create and enforce them.

• Illegal rules are typically created by individuals or organizations in positions of authority or power.

• Government bodies, legislative bodies, or regulatory agencies may be responsible for creating illegal rules.

• Enforcement agencies, such as the police or regulatory authorities, may be responsible for enforcing illegal rules.

• Individuals who knowingly break the law by creatin...read more

LRU Cache is a data structure that stores the most recently used items and discards the least recently used items.

• Use a doubly linked list to keep track of the order of items in the cache

• Use a hash map to store the key-value pairs for fast access

• When an item is accessed, move it to the front of the linked list

• When the cache is full, remove the least recently used item from the back of the linked list and the hash map

I have implemented various technical improvements in codes to enhance performance and functionality.

• Implemented caching mechanisms to reduce load times

• Optimized database queries for faster retrieval of data

• Introduced error handling techniques to improve code reliability

• Utilized design patterns to make the codebase more maintainable

• Refactored legacy code to adhere to best practices

The best way to keep a man alive is to ensure he has access to basic necessities like food, water, shelter, and medical care.

• Provide access to clean drinking water

• Ensure a balanced and nutritious diet

• Provide adequate shelter and protection from the elements

• Ensure access to medical care and treatment

• Encourage regular exercise and physical activity

To be a good data analyzer, one needs to have strong analytical skills and attention to detail.

• Develop strong analytical skills through practice and training

• Pay attention to details and look for patterns in the data

• Use tools and software to help with data analysis

• Stay up-to-date with industry trends and best practices

• Collaborate with others to gain different perspectives on the data

• Validate and verify data to ensure accuracy

• Communicate findings clearly and effectively

Spark is a distributed computing framework used for big data processing.

• Spark is an open-source project under Apache Software Foundation.

• It can process data in real-time and batch mode.

• Spark provides APIs for programming in Java, Scala, Python, and R.

• It can be used for various big data processing tasks like machine learning, graph processing, and SQL queries.

• Spark uses in-memory processing for faster data processing.

Yes, learning goals are essential for personal and professional growth.

• Learning goals help in setting a clear direction for learning and development.

• They provide motivation and focus to achieve desired outcomes.

• Examples of learning goals include improving communication skills, learning a new language, or mastering a new software tool.

• Learning goals should be specific, measurable, achievable, relevant, and time-bound (SMART).

It's impossible for an elephant to die from an ant.

• Ants are too small to cause any harm to an elephant.

• Elephants have thick skin which protects them from insect bites.

• Even if an elephant accidentally ingests an ant, it won't cause any harm.

• This question is likely a trick or joke question.

Design a system for proximity service

• Utilize geolocation data to track user locations

• Implement algorithms to calculate proximity between users

• Use real-time updates to notify users of nearby contacts

A class in Java is a blueprint or template for creating objects that define the properties and behaviors of those objects.

• A class is a fundamental building block in Java programming.

• It encapsulates data and methods that operate on that data.

• Objects are instances of classes.

• Classes can be inherited to create new classes with additional or modified functionality.

• Example: class Car { String color; void start() { ... } }

MVC (Model-View-Controller) architecture design pattern separates an application into three main components.

• Model: Represents the data and business logic of the application

• View: Represents the UI components of the application

• Controller: Acts as an intermediary between Model and View, handling user input and updating the Model accordingly

Implement a key value store for storing and retrieving data efficiently.

• Use a hash table or a balanced tree data structure to store key-value pairs.

• Implement functions for inserting, updating, deleting, and retrieving key-value pairs.

• Consider implementing features like transactions, concurrency control, and data persistence.

• Example: Implement a simple key value store using a hash table in Python.